How to help a friend who's cutting?

So over the weekend I found out my ex-girlfriend who I'm still on good terms with has been cutting herself. She's still in high school and I'm a freshman in college but I visited over the weekend and we hung out yesterday and I noticed she was wearing a bunch of bracelets and I saw the cuts under them. Honestly we were always a better couple than friends and tended to confide more in our friends than each other but since we broke up I found out she's been having some suicidal thoughts and almost no sense of self-worth. I tried pulling her away from her family when I was over to talk to her about it but she avoided it as best she could and I never got a good enough look at the cuts to see how bad or how many there really were so I just tried to push the fact that I'm here to help her and she can talk to me about what's going on and that I wouldn't tell anyone. The thing is that I might be part of the problem because I broke up with her but it was somewhat mutual? If that makes sense she had problems with me being away in college but after we broke up she wanted to get back together but I was hesitant cause she hooked up with her best friend the very next day after we broke up and now I don't know what's up or how she feels about that or where she stands now but I might be ranting. I'm just not sure what to do. I feel like if I tell her family they'll hound her about it and make things worse at home but at the same time she isn't talking to me so that might be the only way I can try and help her. Her sister tends to flip out and be overbearing so that will cause more drama and she'll most likely tell her parents about it. I'm kind of hoping this is an isolated thing but I'm just not sure what to do exactly. Just looking for any advice on what I can do to help.

Thanks