Firemantino, this is a tough call for anyone. If you feel certain she will drink again after getting a new liver, I personally would let her drinking history be known to the transplant team in some way, along with your feeling that she would drink again after a transplant. But this is something you must come to terms with yourself.
Firemantino, I am sorry you are having to deal with these issues, your mom being so sick and the drinking concerns. Sad to say some people do go back to drinking after getting a new liver. I wish you all the best with helping your mom and trying to figure out what to do. It will not be an easy road to travel, you will do what is best for her and you I am sure.