I also have a suicidal friend so I understand

You have to make her realize how much do you love her , give her time . Talk to a therapist about this , even if you try your best it won't be enough to heal her depression "only" a profesional can help her . You have to play a very important role . Try to be with her as much as you can . You said that she doesn't want to accept your help , I have talked to so many depressed people and there was one thing which was very common . Most of the depressed people prefer to be alone , it gives them confort but actually it worsens their mental health . Explain it to her , it's not gonna be easy . But belive me it's not imposible too

Ik you love her and now she needs you the most .