how to stop girlfriend from self-harming

my girlfriend suffers from depression and to cope with it she self-harms. I've tried to get her to stop from doing it because it' not healthy and it hurts me seeing the scars left from it. I know that it's not easy for her and the urge to self-harm is really strong but how do i get her to feel more happy and not to self harm? I really want to see her smile genuinely again.