Why is my roommate so cold to me?

So, about my igned roommate. It's my freshman year of college: I always try to be nice and friendly to her, ask her if she wants to come when I'm going out, etc., and she's nothing but cold and distant. She ignores me or comes up with some condescending answer to what I'm saying. She won't do anything with me--even if we're going to dinner at the exact same time she pushes ahead of me or stalls behind so I can't walk with her. She seems to think my entire outlook on life is stupid, just because I have a more positive attitude than she does. Why is she so cold? What can I do?