As others have alluded to, "functional" is not a type of alcoholic but a stage of alcoholism. It progresses. How fast can vary from person to person, but it will certainly get worse, not better, untreated.
Also, working on communication with an active alcoholic is futile. You are trying to communicate with someone who simply can't.
I know these things because I had to learn them myself. I also had to learn that I could not talk sense into him and get him to stop. I spent years of my life trying.
It is really tough to accept that it is out of your hands what she does. But, once you accept that, you can then begin to make choices based on what you can control--you. I second the recommendation of "Codependent No More." I had to read it three times before it began to sink in, but once it did it was a tremendous help. Another thing that helped me to sort out his problems from my problems was individual counseling.
Best wishes to you and your family.
L
Oh, and as an adult child of an alcoholic myself, I agree that bringing another child into this situation is not a good idea.