She's an intelligent and dedicated student, but is the sort who can't pay attention for too long - she likes learning for learning's sake, but it needs to be on her terms rather than arbitrary, and she doesn't place too high a priority on school if she doesn't enjoy the subject or see the point, which might put her on the outs with some Ravenclaws.
She's a dedicated leader, but she prefers straightforwardness to cunning, bursting in to save the day over espionage, and she doesn't have the drive for power or instinct for self-preservation that are hallmarks of Slytherins.
She closely aligns with Hufflepuffs in terms of ideals and would fit in rather well, but she really lacks patience and the gentleness that sets Hufflepuffs apart.
Kassi is the kind of character who's always on the go, and I feel like she exemplifies the Gryffindor ideals: courage, determination, strength of will. Her lack of patience can sometimes get in the way and lead her to make dangerous mistakes -- there's no time like the present to solve a problem, and leaving things until tomorrow is intensely aggravating.
More importantly, she would choose Gryffindor while the Sorting Hat attempted to place her. Active choices are even more important than passive traits, and Kassi would identify most with Gryffindor and insist on choosing her place.
The Scarf of Sexual Preference says: Waiting 'til Marriage.