She has olive skin and dark brown eyes. Naturally slim and tall, Fiona wears form fitting clothes. They are mostly hand-me-downs or "borrowed" from the store (worn with the tags still on). Her hair is shoulder length.

Fiona is a true South Side girl: she's scrappy, resourceful, and not afraid to get into a fight. As the sole provider for the Gallaghers, she takes on odd jobs (and demeaning ones, like sexy waitressing gigs) to provide for what her father's welfare checks won't cover.