If this is a sincere attempt at recovery (and the tapering off idea makes me question that), she will follow through with it regardless of what you do or don't do. If it isn't, she is going to kill herself drinking whether you are there or not. Seeking peace for yourself, and some distance while you work through what you want, is not cruel; she is a grown woman who can tackle this problem herself if she is motivated to do so.
I'm glad you found us here. Please keep posting and read all you can stand from the Stickies and other daily posts. Welcome!