Fiona Frizzle

"So that's Fiona Felicity Frizzle, huh? Well, that's total Frizzle overload after all. Now what? It's when her older sister gets to be replaced by her just as she now works as a professor in Walkerville College back then."

--Su Ji-Hoon, Operation: Invasion Der Zukünftigen Akademie

Fiona Felicity Frizzle (voiced by Kate McKinnon) is the very beautiful younger sister of Valerie Frizzle and John Frizzle.

Upon her arrival, the entire class greets her as "Ms. Frizzle!" except for Arnold, who tells her "You're not Ms. Frizzle!" to which she replies "Oh, but I am, Arnold."

At first, Fiona seems to be more concerned about the safety of the ecosystem and not as concerned about the dangers and perils that befall her and the class while they're on their field trips. Fiona is (somewhat presumed to be) only 7 (seven) minutes younger than Valerie as they are twins.

Compared to Valerie, she has a more youthful physical appearance, similar to that of an average 25 (twenty-five)-35 (thirty-five)-year-old, while Valerie's is more of an appearance of a middle-aged person. While her outfits do reflect the theme of the day, they are not nearly as flamboyant as her sister's clothes.

She typically wears a long-sleeved purple shirt, red ballet flats, and a necklace/skirt that showcases the theme of the day. Conversely, she might spend the entire episode in special gear like an astronaut suit, or a snow suit. Her theme colors are blue and purple.

In a The Magic School Bus Rides Again episode, Magnetic Mambo, she is shown to be a talented dancer.

In When the Cold Breeze Blows Away, she is the part of Team Magic School Bus.