Bad friends

I can see how the loss of privileges for 24 hours can work. What if a friend of your kids is a "bad" friend…as in giving your kid drugs, cigarettes, etc, or secret things that your kid doesn't want to talk about, or text messages that are inappropriate and ultimately lies about or deletes conversations. How do you go about removing said friend? Can I have my daughter no longer be allowed to speak or hang out with said friend? Is this too much of a consequence? (We homeschool (she's almost 15), so this stuff actually has gone on at youth group and my kids friends group continues to be people I dont want her associating with…ie kids who cut themselves, have eating problems, do drugs/alcohol, talk about killing themselves, talking and looking at sexual things, etc.- her therapist said all this is very normal and I cant take away these friends nor should I be punishing her for now doing these things because she has depression/anxiety/and ptsd from some unforseen circumstances) I'm at a loss…please help!