What should you do if you try to end a relationship and she threatens to commit suicide and then does it but you find her and intervene?
Well, if you intervened, she didn't commit suicide. And she got what she wanted, your full attention. Get professional help for her immediately. You don't need to go through life with this hanging over your head.
I believe you shouldn't commit suicide from bullying/cyber-bullying, people who attempt suicide, but don't commit it often are glad they didn't complete suicide, it only gets better from there. Plus people will be sad if a person commits suicide because they will lose a friend or a family member or whatever relationship they have going on.