Sorry that you're having problems dealing with this. As PP said, AlAnon might be a good thing to look in to.
My own mother has had similar problems in recent years and although *I* know what a great person she has been in the past and could still be, DH only has this awful representation of her.
After many tearful debates, we came to the conclusion that family is family. If they fall off the wagon, you should help them back on but don't let them pull you off the wagon either. You have to have balance.
You guys should talk to her. Maybe she doesn't realize how her decisions are hurting you.
Good luck and Happy Holidays!