How can I have my girlfriend stop this habit? (detail inside)

Well…As some may know I have a girlfriend, I love her and I plan to be with her for….forever..But she’s had big issues in her life…She has a bad family, she hasn’t lived a good life up until she met me…Or so she claims…But she cuts herself and is suicidal, but I prevent her from killing herself….There’s been…SO much going on…I can’t handle it with out me sort of crying in the inside, it’s emotional and I don’t like her cutting herself or trying to suffocate herself…She’s promised me to stop all this…But as I know..and I’ve read, a lot of people can’t seem to stop sadly… But I have changed her life dramatically. Please fluther, for the sake of me, and maybe even a life at danger from herself…Please…how do I stop this? I don’t like knowing that something may happen (natural disaster, someone taking her, killing her from an unknown figure, etc…) that will kill her…And knowing that she wants to kill herself. Please, help me, I’m with her because I love her with all my heart, I don’t want anything to happen to her, I don’t want her to harm herself anymore or keep choking herself anymore. I’m in desperate need. Please again. Thank you…(Also friend of hers died today from a horrible car crash Junetha Crystal Centeno aka JC. May you R.I.P.)