When would you give up on trying to help somebody?

I have a friend I’ve known for about 5 years now. She has always been depressed, constantly trying to harm herself and in and out of hospitals. She got addicted to drugs and was in rehab but still does some of them. She’s in the hospital for another suicide attempt.
This has got to be her like 9th or 10th attempt, as I said she never stopped with the drugs. I love her and I do believe that everyone is worth saving, but it is getting hard to deal with. I feel bad when she does this and I don’t check up on her enough, and I obviously don’t want her to die.
How can somebody be getting so much treatment for various things, be put on medication, in therapy multiple times, and all that, but still be the same person and never change? She’s gotten a lot of help but still goes back to her old ways.