What a sad story. I am so sorry about your Mom. I'm sure you did what you could, but in the end, it was her choice, not yours. You can't just snap someone out of it. Try to let go of your guilt. She obviously loved you very, very much. She had a disease, alcoholism. You couldn't treat her anymore than I'd she had cancer.
And remember she loved you very very much. Much hugs and prayers for you. Bless.