The way you keep trying is by continuing what you have started: educating yourself on addiction and following expert advice on how best to help an addict.
The expert advice is to stop rescuing the addict from any consequences of using drugs so that the addict can experience enough pain and crisis-- caused by drugs --that the addict wants to QUIT.
Yes, you should keep trying, and the way you do that is to continue to educate yourself about setting boundaries and refusing to enable.
The addict will continue to use as long as she is rescued from the problems drugs create in her life.
You are definitely helping her in the right way today if you are keeping hands off her problems.