Let her go*....especially now if she has suggested a break up and is currently drinking. If you two are just dating and aren't married yet--I would say let her do what she is going to do and move on with your life. As an alcoholic in recovery, I will say that while drinking--alcohol always came first. Just know that whatever you decide to do about this situation--you didn't cause it, can't control it, can't cure it-----her alcoholism. You can't save her from her disease. If you do decide however, to stay involved in this relationship, I would suggest going to Alanon meetings. They will help you better understand how to handle this situation, but are focused to help you in this relationship.
Welcome to SR! Glad you are here. This is a great place for support.
*Detatchment is what I meant to say.