wow... yikes.. sounds to me like she has taken a dive over to the pain side of the line to me. I think that as a friend, you might gently talk with her and explain to her your concerns. Yes, it is true that some people enjoy LOTS of pain and receive sexual gratification from that, but I would hope to think that pain resulting in blood and scaring isn't something that most people would enjoy.

If she truly considers you a friend, she will accept your concern and share with you her thoughts. Maybe by talking about it, she can figure out another way to achieve the same result without causing herself physical pain, blood loss, and scarring.