Because one: if she does she'll never know if life will get better and it probably will. And two: if she dies think of how many people would be affected and think of those who will be devastated at the loss of her. I don't even know her and I think I would be. I don't want her to kill herself because life is going wrong. I want her to live because it will get better and she won't regret not killing herself later on because who knows what amazing things the future holds? Whatever you do don't let her do this. Be the reason she doesn't kill herself. Be the person who keeps her strong and gives her a chance to live. Don't let her go. No matter what.
tell her he'll be hurting many people just by trying to make herself feel better. That's sort of selfish. Also say that you would be devastated. She should live because people love her. It would be good if you knew her problem?