The worst thing I ever did for my XAH was giving him chance after chance after chance and not doing what I said I was going to do. I enabled him by not sticking to my boundaries and holding him accountable. That's my disease... Ms. nice Girl.
I did it because I loved him and wanted to help. But that's not help for and addict.
You've been giving some great responses. If you want to help your sister, treat her like and adult and let her deal with the consequences of HER choices.