What to do when your teens friends start to do stupid stuff and drag then into the dramas,emotionally?

so my daughters friend is depressed,suicidal,meeting guys on the internet..my daughter is constantly answering her text pleas of desperation,worrying for her..trying to make her happy..the girls mom is a pill head,don't think I'll get much help there but the involvement is becoming detrimental to my child ..she is manipulated and loyal to being there for her friend ,even to the point of endangering herself..her friend is needy,dependent,whiny and truly does have things hard..I just forbade my daughter to be friends with the girl but I feel we abandoned her too and I think I just encouraged my daughter to lie and sneak more then she did this past few weeks talking to some guy in Fla on her cell, trying to fix a broken myspace relationship for the girl so she won't kill herself...So how to help my daughter see the poor me drama,break the cycle..not feel guilty..help the girl get help if it's possible..Thank you for your input.