Man, that's really some pressure she's putting on you. I know kinda how it feels, my friend cut herself, but i dont remember if i'd told her i cut or not before, but anyway i think i did and i blame myself but i think she did it more as a phase thing because she stopped anyway and thinks that telling me to stop will work but it doesn't happen that way.

I sure hope you can convince your friend that cutting is not the way forward and urge her to get good help!