Bullying. . . . . . . . . . . .?

[Valley Girl]

Okay, so to start things off please don't judge what I said. I did what I did out of anger and disrespect for someone. Well this all stated a week ago with me and my ex-friend. I had told my friend that I did not want my ex-friend to get me into any trouble like she had done with another girl. and I had explain to the friend how she had got someone else in trouble. Well that same day after I got out of school she text me asking me why I was starting rumors about her. I told her that I was not because its not like I went and told 5 people about it. If someone else tells then that them spreading the rumor not me. Well that night I saw her at the football game with her mother watching her( where both in high school) to make sure that I would try not to punch her. But, also that night she told 2 of my really close friends about what happen. I did not confront her about what happen. Then on either Saturday or Sunday she posted a sub-tweet about me (which means she did not say my name she just used words like "chick" or "whore") I am not sure if what she tweeted or what she said I am just saying what people have told me. Now, today I saw her and she gave me ( she quotes) " a death stare that will stop water" I just glanced at her and moved on. Later on today she started talking to my boyfriends friends about what had happen.She also told people about personal things that I told her earlier this year. she is also now telling my friends about my personal Business trying to turn the attention away from herself. What should I do about this girl? And how do I tell her to stop being a bitch without saying your being a bitch.
BTW I have a class with her. How do I act around her now and we have the same group of friends so It will be hard to avoid her.