i guess you cannot change schools? please block this person on facebook so that you do not have to listen to her, but PRINT everything that she said, and take that to school, it is evidence, i am not sure, where you live, but if she is picking on you on facebook that is harassment and you can take it to the Police so that they can tell her she has to stop
Document everything, if you need help you let me know, when i was younger i was bullied alot, and i had an abusive husband, i will not stand by and do nothing if someone is being hurt. Please make a record of everything she says and does, in a journal, and print off anything she says to you on facebook
here is my facebook http://www.facebook.com/adicat if you need some support.
big big hugs
adi