Practice reverse psychology. If you're the clean freak and your roommate is a slob, stop cleaning. If she plays her awful music loudly, bust out your '90s pop on high volume. If she constantly has groups of friends over, you do so as well. If she eats all your food, stop buying it. Acting out your roommate's behaviors for her to see will show her how annoying and unpleasant they can be, and will hopefully spark a change.
Pledge a sorority or fraternity. Once pledging activities begin, you may be required to stay with your fellow pledges in a room either in the dorms on at the Greek house. Once semester hits, you can elect to room with one of your new Greek siblings.
Talk to your Residential Adviser (RA) about switching to a room with a new roommate or a private room. A single room may cost more, but switching to a new room with a different roommate won't affect your room and board costs.