"Excuse me, Phineas. Can I get you to sign some liability waivers?" -Katie
She, along with Ginger, Milly, and Holly help Phineas and Ferb create S'winter ("S'Winter"). She helps build the time machine with the rest of the troop ("It's About Time!"). She and Holly also participated in the Chariot Race with Isabella ("Greece Lightning").
Katie interrupted by asking Phineas to sign some liability wavers just when Isabella was about to ask him to the dance ("Out to Launch").She sold cupcakes to Heinz Doofenshmirtz on two occasions: once with Gretchen and another with Milly ("Don't Even Blink", "Fireside Girl Jamboree"). She somehow got injured as a result of the Fireside Girls' attempt at running a lemonade stand, shown by her hands and part of her face bandaged up. ("At the Car Wash").
Katie has blond hair in two low pigtails with red elastics, green eyes and is light-skinned. She wears a uniform with a red collar with large shoes and no socks.
But in winter, she wears a red sweater with orange kerchef, yellow boots, has brown elastics in her hair, and wears an orange hat. She does not wear leggings in winter, unlike the other girls.
- Help Thy Neighbor Patch (About 52 as of "Isabella and the Temple of Sap")
- Aquatic Safety Patch
- Sewing Patch
- Tent Pitching Patch, Marshmallow Patch
- Aeronautic Patch
- Sap Collecting Patch
- Mountain Moving Patch
- Desert Tracking Patch,
- Rain-forest/Jungle Navigation Patch,
- Rock-climbing Patch,
- Non-power Flight Patch,
- Concussion First-aid Patch
- Flier Delivery Patch (Twice as of "The Remains of the Platypus")
- She and Gretchen are the only Fireside Girls who appear in the Phineas and Ferb Nintendo DS game.
- Before Unknown Fireside Girl (blond) appearance, she was the only Fireside Girl that has blond hair.
- She and Ginger appeared at the opening of Phineas and Ferb's roller coaster.
- Her name was revealed in "Isabella and the Temple of Sap".
- She has been seen selling cupcakes with Gretchen or Milly to Heinz Doofenshmirtz.
- Her first speaking role was interrupting Isabella in Out to Launch, just as Isabella was about to ask Phineas to the dance.
- She is one of Fireside Girls who doesn't wear socks as part of her uniform. The other is Unknown Fireside Girl (brown), from Tour de Ferb.
- In the ending song of "Rollercoaster: The Musical!", Carpe Diem, there are two different Katies shown; the one from the beginning of the Original Rollercoaster Episode, and the Fireside Girl Katie.
- She along with Milly and Gretchen are the only girls to appear in "Disney's Phineas and Ferb: The Best LIVE Tour Ever!".
- She took down a burly man much bigger than her in arm wrestling in the episode Ferb TV.