Isabella García-Shapiro (played by Alyson Stoner) is the neighbor and best friend of Phineas and Ferb. Isabella has a very big crush on Phineas. She is the leader of Fireside Girls Troop 46231, and often volunteers to help in Big Ideas, usually with her troop involved. She is Jewish, although she claims to have written letters to Santa, and during the song, Where Did We Go Wrong?, she is seen singing in front of a Christmas tree ("Phineas and Ferb Christmas Vacation!", "Picture This").
Isabella Garcia-Shapiro was born of a Hispanic mother and a Jewish-American father. At some point in her life, she met and befriended, Phineas and Ferb (with Phineas becoming her crush). She also joined the local troop of Fireside Girls, and became the troop leader.
Now the leader of the Fireside Girls, Isabella lives in Danville on Maple Drive, across from Phineas and Ferb with her mother, Vivian Garcia-Shapiro. She spends most of her days participating or helping with their many projects. She also spends time caring for her dog Pinky or trying to earn Fireside Girls patches. She is also great friends with the members of her Fireside Girls troop, Gretchen, Milly, Ginger, Katie, Holly, and Adyson.
Isabella is happy, fearless, sweet, caring and spirited, eager to help with any of Phineas and Ferb's Big Ideas. Most of the time it's for patches, or simply because she has a crush on Phineas. She is mostly optimistic, but she also cares for, and worries about people at times. Being the leader of Fireside Girls 46231, she has fantastic leadership and organizational abilities, though she'll follow Phineas's orders as well. Isabella can get a little jealous and frustrated at some "thing" or someone that Phineas gives a lot of attention ("The Chronicles of Meap", "That Sinking Feeling", "Summer Belongs To You"). She also didn't like how Melissa showed more interest in Candace than her ("We Call it Maze"). Isabella has shown at least twice that she has a devious streak, taking advantage of a situation for her own benefit. These instances include her immediately jumping on Baljeet's wager of squid versus Buford ("Voyage to the Bottom of Buford"). She also buys a play with the carny Shady Joe when a bowling ball Phineas and Ferb built knocks down all the pins (along with the stand), although Shady Joe is cheating by having the pins taped onto the shelf ("Bowl-R-Ama Drama").
Isabella has long black hair and oval blue eyes. She wears a pink dress with a white T-shirt underneath and a purple belt, white socks and pink shoes. The pink bow in her hair is thought to be her trademark, and she has only been seen without it on a few occasions (see background information). Her Fireside Girls uniform is the same format as her normal clothing, but with an orange top and a brown skirt. She wears an orange beret with a red bow in the front. Her belt is red, and she has an accomplishment sash. She has white socks and red shoes with this outfit.
- Troop Leader Patch (This patch is a miniature version of the Fireside Girls emblem. Only worn by past and present leaders)
- Help Thy Neighbor Patch (About 52 as of "Isabella and the Temple of Sap")
- Aquatic Safety Patch ("Lawn Gnome Beach Party of Terror")
- Sewing Patch ("Run Away Runway")
- Milking Patch ("The Magnificent Few")
- Tonsillectomy Patch ("I Scream, You Scream")
- Tent Pitching Patch ("Get That Bigfoot Outta My Face!")
- Marshmallow Patch ("Get That Bigfoot Outta My Face!")
- Aeronautic Patch ("De Plane! De Plane!")
- Broadcasting Patch ("Let's Take A Quiz")
- Shrimp Net Repair Patch ("That Sinking Feeling")
- I Just Saw A Cute Boy Patch ("Isabella and the Temple of Sap")
- Sap Collecting Patch ("Isabella and the Temple of Sap")
- Expert Makeover Patch ("Cheer Up, Candace")
- Santa's Helper Patch ("Phineas and Ferb Christmas Vacation!")
- Mountain Moving Patch ("Phineas and Ferb-Busters!")
- Rodeo Clown Patch ("Robot Rodeo")
- Intrepid Reporter Patch ("The Beak")
- High Wire Patch (Twice "We Call it Maze")
Isabella has a huge crush on her neighbor and best friend Phineas. She has romantic daydreams about him and believes she will one day marry him but gеts angry if he does not notice her or is oblivious to her hints, which is generally whenever she acts romantically around him ("Phineas and Ferb's Quantum Boogaloo", "Isabella and the Temple of Sap", "Out to Launch", "Comet Kermillian", "Candace's Big Day", etc.).
One example of this is when Isabella and Phineas were alone in Paris looking for parts, and Isabella was trying to be romantic, but Phineas seemed utterly oblivious to her. Then when the boat crash landed on the deserted island and Phineas was trying to find something to fix the boat, Isabella began crying because Phineas didn't even take notice of her and she would've given anything for Phineas to sit down next to her and enjoy the sunset. Then Phineas ran up next to her, having a small mental breakdown, desperately thinking of an idea to get off of the island. Figuring that none of the ideas would work, he gave up hope entirely and sat down with Isabella to enjoy the sunset with her. Seeing how broken Phineas was, Isabella realized that this wasn't the amazing kid she had fallen in love with, so she gave him a pep talk, and almost admitting her love for him in the process, but she quickly caught herself and said something else. She then mentioned Ferb's map and Phineas thanked her for the inspiration with a hug, leaving her in a trance. Later when they make it back to Danville, Isabella hugs Phineas for regaining his confidence to achieve his goal. Not even 30 seconds later they sing a duet (Summer Belongs to You (song)) with Phineas taking her hand several times and also showing several signs that he returns her feelings for him ("Phineas and Ferb: Summer Belongs To You!").
However, when Phineas constructs a device to find cute things to search for Meap, he says he took Isabella's cuteness into account and adjusted the settings accordingly ("The Chronicles of Meap"). When he puts the settings back to normal, the device overloads from an excessively strong cute signal. She uses her position as Fireside Girls troop leader to stay near him and participate in his Big Ideas, under the guise of earning the "Help Thy Neighbor" patch. It is unsure whether Phineas has the same feelings towards Isabella, but mostly he seems oblivious. Phineas feels bad about ditching her, and also says that he cannot tell her he is The Beak because she is "close to him" ("The Beak"). Also, when Isabella tells Phineas he is brave, he replies with, "You were too!" She learns that she will be aunt to Candace's children. Although who she married was unknown, it will likely be Phineas, since Phineas is now being shown returning Isabella's feelings. She sometimes disguises her affection for him (but very rarely) like hugging him in a crowd when everyone is hugging Perry Isabella hugs Phineas instead ("Oh, There You Are, Perry").
Isabella is good friends with Ferb, likely because he's the stepbrother of her crush, Phineas, although she seems to get annoyed when Ferb goes wherever Phineas does. Along with Candace, she has outright stated that Ferb is Phineas' stepbrother ("Rollercoaster"). Unlike her relationship with Phineas, Isabella shows no romantic interest in Ferb. However, after time-traveling to the future, she learned that she might marry Phineas or Ferb ("Phineas and Ferb's Quantum Boogaloo"). Upon this discovery, Ferb turned around and winked at Isabella, who was stunned at the possibility that she may marry someone else other than Phineas. This may indicate that Ferb may harbor a bit of affection for Isabella, or that Ferb just fancies himself a ladies' man ("Thaddeus and Thor"). It is also possible he was simply teasing her. Ferb is slightly irritated when Phineas gets all of Isabella's attention and praise for being a superhero ("The Beak"). When they were stranded on the island, Ferb listened while Isabella talked about Phineas not noticing her, and offered her a handkerchief when she started crying. He knows about Isabella's crush on Phineas. ("Phineas and Ferb: Summer Belongs To You!").
Isabella is friends with Baljeet. They hang out on occasion, usually when they are brought together by Phineas and Ferb's Big Ideas. She won a bet against him on who would win the fight between Buford and the squid ("Voyage to the Bottom of Buford"). Though when trying to find the purpose of a machine Baljeet did jump at the chance to have a romantic dinner with Isabella, even a staged one, suggesting some romantic interest towards Isabella ("What Do It Do?"). This is also hinted when Baljeet asked Isabella if he made a good Phineas, she responds with "No, no you weren't" ("Not Phineas and Ferb").
When they play sports or games, Buford usually mocks her for being a girl, and therefore less of a competitor in his eyes. Isabella takes this very seriously and refuses to let Buford beat her ("Got Game?", "Brain Drain"). When she saw Buford crying about his lost goldfish, she expressed concern and worry about him ("Voyage to the Bottom of Buford"). She also stood up to the video-game boss (designed in Buford's image), and defeated him after he threatened Phineas ("Gaming the System"), though technically this was not the real Buford.
Isabella and Candace are good friends. They both know about each others' respective crushes and share advice and experiences ("One Good Scare Ought to Do It!", "Out to Launch", "Phineas and Ferb's Quantum Boogaloo", "Phineas and Ferb-Busters!", "Phineas and Ferb: Summer Belongs To You!"). While in Paris, Isabella felt jealous of Candace's relationship with Jeremy ("Phineas and Ferb: Summer Belongs To You!"). When Isabella excitedly realized that Candace's future daughter called her "Aunt Isabella", meaning that she married into the Flynn-Fletcher family, Candace reminds her that she could marry either Phineas or Ferb as a counterbalance ("Phineas and Ferb's Quantum Boogaloo"). Candace teamed up with Isabella to beat Buford and Baljeet ("Got Game?"). Isabella also helped Candace get a ticket to the Paisley Sideburn Brothers Concert ("Fireside Girl Jamboree"). Even though they like each other in general, Isabella was mad at Candace when Melissa was more interested in Candace's achievements than Isabella's, yet they became reconciled when Candace admitted that if it had not been for Isabella, she would have never gained 50 Accomplishment Patches in a single day ("We Call it Maze"). Interestingly, Candace doesn't try to bust Isabella in Not Phineas and Ferb.
As the troop's leader the Fireside Girls always follow Isabella's orders, always ready and willing to do whatever it takes to help their leader in helping Phineas and Ferb, even risking themselves to do it. Although the girls are loyal to Isabella, and have earned many a badge in helping the boys, they have voiced that they've collected more than fifty of the 'helping thy neighbor' badge because of it. They're also aware of Isabella's crush on Phineas and her desire to marry him, and they jokingly tease her for it ("Isabella and the Temple of Sap"). Even so, they remain friends with the boys and squealed with delight when Phineas invited Isabella on a romantic cruise ("That Sinking Feeling").
- Isabella is an excellent singer ("S'Winter", "The Magnificent Few", "The Ballad of Badbeard", "Phineas and Ferb: Summer Belongs To You!", "Wizard of Odd" and in several other episodes). Also in several of the songs, you can hear her singing alone. (Where Did We Go Wrong?, City of Love, We Wish You A Merry Christmas, etc.)
- Isabella appeared as the good witch in "Wizard of Odd." During that episode, she wore a pink dress with a pink tiara and wand. She traveled through a floating eyeball and her friends as the good witch were the patchkins.
- She can whistle with two fingers ("S'Winter").
- The character is named after series creator Dan Povenmire's oldest daughter who loves the show and enjoys that Isabella is named for her.
- Isabella owns roller skates ("Bowl-R-Ama Drama").
- Isabella has a pool in her backyard ("Rollercoaster", "Ready for the Bettys", "Day of the Living Gelatin").
- Isabella has a chihuahua named Pinky who is revealed to be a secret agent in the O.W.C.A. like Perry ("Journey to the Center of Candace", "Comet Kermillian", "Interview With a Platypus", "Day of the Living Gelatin", "Hide and Seek", "Isabella and the Temple of Sap").
- Isabella could be descended from a girl that looks exactly like her, who was friends with Dr. Phineastein and Ferbgor ("The Monster of Phineas-n-Ferbenstein").
- Isabella can play the tambourine, ("The Fast and the Phineas", "Don't Even Blink" and in other episodes.) the trumpet, ("Don't Even Blink") the guitar and the key-tar ("Tip of the Day", "Gaming the System", "Oh, There You Are, Perry" and in other episodes).
- Her mother, Vivian Garcia-Shapiro calls her "Isa" for short. This is a common shortening of her name in many Spanish-speaking countries ("Hide and Seek").
- Her signature look and her Fireside Girl uniform switch on occasion ("Flop Starz", "The Fast and the Phineas", "Candace Loses Her Head", "The Flying Fishmonger", "At the Car Wash", "Candace's Big Day", "Robot Rodeo").
- She is the leader of Fireside Girls Troop 46231 ("Isabella and the Temple of Sap").
- There is now plenty of evidence that Isabella is at least part Jewish. Her last name is Shapiro, traditionally a Jewish name. She has a mirror in her room that has a Star of David frame; this is a common symbol for Judaism. Also, Isabella's mother, Vivian Garcia-Shapiro, went to a Mexican-Jewish Cultural Festival and often uses Yiddish phrases. Isabella says she celebrates Hanukkah instead of Christmas ("Isabella and the Temple of Sap", "Picture This", "Phineas and Ferb Christmas Vacation!").
- She is able to tell when someone else says her catchphrase, "Whatcha doin'?", even when she is not near the person. She gets very upset if someone says it except for Phineas, ("I Scream, You Scream", "At the Car Wash", "That Sinking Feeling") and she does not let anyone say it to Phineas ("Out of Toon", "Suddenly Suzy"). She also feels a disturbance whenever somebody else says it ("Phineas and Ferb Christmas Vacation!"). Baljeet says it once to Phineas, but Isabella was not around and he said, "I sounded just like Isabella" ("Bowl-R-Ama Drama").
- She is the only one of Phineas and Ferb's main group of friends that hasn't been seen at a younger age yet.
- Isabella knows how to drive a van ("Isabella and the Temple of Sap") and a jet ("Phineas and Ferb Christmas Vacation!"), but she agreed with Phineas that she was too young to drive ("The Secret of Success").
- She is a strong girl as she is seen that she can hold Phineas in her hands ("One Good Scare Ought to Do It!"), can actually hurt Buford (a very tough bully) just by elbowing him ("Out of Toon"), can lift a book that is much larger than her ("Fireside Girl Jamboree"), with Baljeet's help, lift the seats from the Sun-Beater 3000 onto the paper airplane and is seen breaking a pencil ("Phineas and Ferb: Summer Belongs To You!").
- She is a very fast runner. ("Candace Loses Her Head", "Journey to the Center of Candace")
- She knows a lot about cars and engines ("The Fast and the Phineas", "The Secret of Success").
- She can use a much deeper voice, which can scare an unprepared listener ("It's a Mud, Mud, Mud, Mud World").
- She can dance well, almost based on her voice actress ("Robot Rodeo"). She has also danced in "Put That Putter Away", "Day of the Living Gelatin", "Spa Day", "Fireside Girl Jamboree", and other episodes.
- When her hair is exposed to humidity, it frizzes ("Robot Rodeo").
- She seems to have an obsession with horses, especially brightly colored ones or unicorns ("The Magnificent Few", "Hail Doofania!", "Isabella and the Temple of Sap", "Ain't No Kiddie Ride").
- She reads the newspaper ("Phineas and Ferb Christmas Vacation!", "The Beak").
- She has been seen without her bow on a few occasions: as a pirate in The Ballad of Badbeard, as a "ninja of love" in the performance of "You Snuck Your Way Right Into My Heart" ("Dude, We're Getting the Band Back Together"), in a horse costume ("Got Game?"), wearing a fedora ("The Beak"), in foreign costume during the song "Bouncin' Around the World" as well wearing a beret in "City of Love" ("Phineas and Ferb: Summer Belongs To You!"). There was one day where Isabella never wears her bow ("The Beak"). (Of course, it may be under her hat).
- She gets jealous when all credit or attention is taken away from her. ("The Chronicles of Meap", "That Sinking Feeling", "We Call it Maze")
- She has kind of a short temper. This was showed in various episodes including "Phineas and Ferb: Summer Belongs To You!" when she broke her pencil out of anger.
- She owns a Mindy doll. ("Picture This")
- She was once a member of the Lil' Sparks and now tutoring Melissa. ("We Call It Maze")
- In Candace's dream Isabella was the Good Witch. ("Wizard of Odd")