What to do about this girl?

okay so this girl who is a big jerk found out im a cutter :/ and she is threading to tell on me so i decided to be friends with her and shes bin really mean to me lien to me trying to get me jealous and blah blah blah shes half the reason i cut and i wanna tell her i don't wanna be her friend anymore cuz she keeps texting me and if i don't respond she will keep texting me she might tell if i say i don't she will tell everyone i cut what to do