My theory on "Cinderella" is that she's a 'normal student' who, aside from attending DIK/HOT parties and being 'friends of friends' who get them into said parties, has no connection to any of the main cast and represents the various random background characters who don't have parents who work/run B&R, aren't sexually involved with anyone running Greek life, etc. and simply go about their daily lives being semi-oblivious to all the drama going on in the administration building and the frat/sorority houses.
Her path could be her showing MC that there is a life at college beyond Greek life and studying.
Sage: Hey, MC, are you coming to the HOT party on Friday night?
MC: Oh, actually, Nikita is taking me to a meeting of the college Republicans Friday night, and then we're going to a movie.
Sage: Oh, okay. Well, that sounds pretty lame, but have fun, I guess.