Should I still be friends with her. ?

If other people also know, slip her mom a note. Send her a letter in the mail or tell your mom and they will talk about it. Also, you really should find a new best friend. I'm 21 now and since I was 12 I have gone through 3 completely new sets of friends. Sometimes you have to give certain people up in order to make sure your life doesn't go downhill. You are so smart at 12 years old to be getting away from people like that. If she is actually your "friend" she would give it up so that ya'll can keep your friendship. Talk to someone else at school tomorrow :)