bad friends make bad memories... and they just don't want to stop! Advice?

ouuggggh, I can't stop shaking. I hate her so f*****g much it makes me want to break something!!

So, about what am I talking about? About that girl from our town that was once my friend, but than I noticed she just wasn't what I expected from a friend to be and we got into a fight and she really did some nasty things to me, like made me lost my job and embarrassed me in front of all the people on face book, saying I am a whore (that I literally had sex for money). So, that was in summer and I almost forget about it and move on with my life, although it still makes me angry when I think about it.
In that fight I also lost my good friend (at least that is what I thought he was) and that really hurt. I thought that after all this time I could try to make some connections with him, so I wrote to him, but I made a mistake. He is a very good friend with that bi**h so they tried to use that against me.
Today I found out that they are making a plan of how to destroy my life completely although I haven't done nothing to either of them. That just got all back on the track... all the memories from the summer, all the anger, sadness, everything. But OK, I decided to not to think about them, they don't have any connection with me, so what the hell can they do, right?

But when I came on the face book, that b**ch wrote to me, trying to make a contact with me and since I know about that plan they're making I wasn't really into chatting with her. But that she started to talk about my sister, she is 3 years younger than me and she goes to the same school as that bi**h is going. She was talking about how beautiful my sister is, that she looks much batter than me ans so on and that I should say hi to her and stuff like that... and that is what got me scared. I will try to convince my sister not to talk with her or something and I know she'll understand, since she was watching everything that happened in summer, but I am a bit afraid... is it possible that she is so mean? I mean that she would destroy somebodies life just because she's bored? I mean, that's just sick!

I really want to ignore it, but what she did to me in summer was just waaaay to cruel and I'm afraid of what she has in plan now...

What should I do? Any advice? Please?