Cutting and self injury in general is a sensitive matter, especially with the way it's viewed in society today. Most people are quick to dismiss anything of the nature as "emo," or some desperate attention whore's plea for the public eye. There are definitely fine lines between a true problem, a cry for attention, and a mixture of both... and sometimes even those who self mutilate for the same reason others get tattoos and piercings.
Self mutilation is, for most, an addiction comparable to drugs. It's a very serious addiction, both physically and mentally. In most all cases, it requires medical attention. From what you've said, your friend has gone through treatment without success. Like a drug addict, she won't ever change unless she wants to change.
There isn't much you can do, really. Be her friend, listen if she needs it... Try to reinforce the idea that she needs help, and that she needs to change. Just know that no matter how hard you try, nothing will change unless she wants it.
If you feel that you are fueling her addiction, politely excuse yourself from the situation and don't make a big deal of it. If you feel that it requires attention, but don't feel it's your place, notify those who need to know, and then stay out of it any further.