First off, do you actually like the girl or are you just with her because there's no one else?
Your experience is standard uni experience. The girl became 'friends' with you before uni started for the same reasons as many others- she wanted to have a ready made friend so she didn't have to face uni alone, and face the daunting prospect of not making any friends. So even if she doesn't make any friends on her course, she has you at least. And I expect you are feeling quite similar, you don't really get on with her (how could you, she doesn't sound very nice) but she's a 'friend' and it's better than being alone?
It's not just you, this happens loads during freshers. People make 'friends' but they aren't friends, they're just people you cling to (so you haven't got to be alone) until you find people you actually click with. She's done that, in albeit, a more harsh way. I think it's a ****ty thing to do yeah, but what I'm trying to say is, it's not just you, it's not because of how you are, you just weren't meant to be friends.
You sound a hell of a lot better than her anyway. So you need to learn to NGAF, and to only want to be friends with people who actually add to your life, and make you happy. Because that's what you deserve, no less. So **** her, go out there and meet other friends, and join societies to find like minded people. Uni is a tough ride, and not the social experience half of us expect it to be, you've just got to be strong and persevere until you find people who make you feel happy.