I used to bartend and my manager there had a small rectangle of paper stapled to a beam next to the register. On it it read:

Before trying to change someone; first consider how difficult it is to change yourself.

I lived with an abusive alcoholic/cokehead for 9 years. I tried. Again and again and finally I realized he wasn't going to quit until he wanted to. I left him.

I'm so sorry about your sister, it must be so hard wanting to help, wanting to fix and being rebuffed. All you can do is either keep trying or give up. Enabling her helps keep her an addict. Only you can decide how you want to handle this.

Hang in there.