I don't know the past history or what your area laws are but you could check and see if you could petition the courts for a court order forcing her into treatment. While this may not be successful there is a small chance that an opportunity to sober up for a long enough period of time may (repeat may) result in her realizing her need to remain in treatment and recovery.
If you do not have local laws or support for this you could try an intervention where you and any other persons who care about her can give her a final ultimatim of what she would have to do in order for you to remain in her life. If she refuses then she will have cut the ties and you would feel better about the decision to not participate or watch her kill herself slowly.
I recommend Debra Jay's book NO MORE LETTING GO for a very thoughtful,, balanced and helpful guide to a well thought out and balanced intervention process.
Remember that even if you go above and beyond to ridiculous lengths it will not be successful unless she decides that she truly wants to be sober for life no matter what it will take to accomplish that goal. That being said... you never know if a failed intervention isn't seed for the future when she may come to realization that she does want to live a life of recovery