Before I try to help, I just want to state I have no Idea what you all are going through, and I'm sorry if I offend anyone, but I had a suicidal friend before, and I want to help people with it.
Listen to me, as long as your there for her, she will be ok, just keep faith, even if you have none, you have to listen to me. You need to keep hope, if you don't have hope, she wont. YOU CAN GET HER THROUGH THIS, and if she does, you will too. Nothing makes you feel more important than keeping another person alive. I've dealt with a situation like yours before, it was with a close friend of mine. I know how you feel, it was extremely stressfull, I felt like giving up, but I didn't, and he got through it. The point is you can't give up on her or yourself, and doubting yourself makes it harder. Be there for her, and stop blaming yourself for ruining peoples lives you come in contact with. It's not your fault. I'm sorry I can't help more, but I'm not in your situation. Now trust me, as long as your there for her, and stay confident in your support, she can get through this. Please just believe in yourself.