You said so yourself: she's done it before, which means she'll do it again. While she's causing social ostracism for you, the people will eventually see the other side of her too, and so this probably won't last forever. She's only going to alienate herself in the end. In the meantime, I'd really do my best to stay away from her but at the same time not show any hostility towards her. These people are very easy to set off and any attitude that is the least bit threatening or shows rejection in any way will backfire. If you really feel like you can't escape this then I would seek some more help ; maybe contact her parents or ask your counselor if there's anything else that can be done. Worst case scenerio, I'd transfer to a different University, but I also think that you shouldn't have to do that. So it's up to you.