This is a potentially abusive relationship. Let your school know about the situation and that this person is not welcome near your child. Second record all incidents (just like the poster said, time dates witnesses).
Also, she has no right to speak to your daughter. If she comes near your daughter you have every right to call the police, no matter what she says.
Unless she has a child at the school she has no right to be there and do let the school know.
Explain to your daughter that she is not to talk to her no matter what. Cut the ties from her and don't take any crap. If she has a key change your locks. Be careful not to get yourself caught in this web of drama, it can be dangerous. Dont feel like you have to take this from her, you dont.
Write everything down and contact the police. They can give you more advice and help direct you.