I think that I would talk to her about what is going on. I would tell her that you are not willing to raise her in a home with an alcoholic who is drinking. Explain that you love her too much to let this happen.
Tell her that you have told Dad that if he drinks alcohol in your home, that you won't be staying. My daughter is pretty worldly-wise at 11, and she would be likely to argue with me, so be prepared for that.
He will also be playing on her sympathies, so it's important that you let her know that Dad knows the rules of living with y'all, too, and has been told what to expect.