What to do about my roomate in college?!?

Ok, so I'm going into my sophomore year in college and I'm rooming with my "friend". The thing is, she's only 18 but LOVES drinking/partying, even though she doesn't look like a party girl at all. And nobody wants to invite her to parties (she tags along with me). She has very high tolerance to alcohol, and her main mission is "to get wasted". This July I'm turning 21, so now she tells me " you're gonna be my alcohol provider". There's no freaking way that I'm going to buy her booze so that she'll get drunk, because this year is going be hard for me and I have a lot of commitments (job, clubs, applying for study abroad, etc.). How can I get her off my head? I can't switch roomates, but I refuse to be taken advantage of. Plus, she's really annoying. One time I didn't feel like going out, and she said " Oh, you're so boring". Even though it was probably the only time I said no to her. Please help!