I have tried avoiding this girl, and now she thinks I am mad. What to do?

The only reason to confront her is if you think there is a friendship that is worth saving. But if not, then there is no sense in confronting her about it. She will just get pissy and possibly even more confrontational and vindictive. Just tell her you are tired and it's been a long day and you want to go home. If she keeps hounding you then you may have no choice but to talk to her. But for me, I wouldn't confront somebody about that type of thing. If it was a boyfriend/girlfriend, then I feel I owe them a clean break. But just an acquaintance at school who gets on my nerves? Naw, it's not worth the headache. Just avoid her when you can and when you can't, just smile and nod. Say as little as necessary to her and respond to her recent text with "just busy, sorry". It may take awhile, but I am sure she will get the point.