The best way i have learned to deal with family and friends that suffer from the disease of addiction is through healthy boundaries. You cannot control her or really do anything that will keep her sober. Maybe the best course of action is for her to go through an intervention of some sort. Interventions can be gentle and full of love if done properly. I recently had to participate in an intervention for my brother. My family found this guide online
Intervention Guide - Recovery Connection and found it extremely helpful in giving us a foundation on how to go about it.
It is not to late for your fiance to get help. An intervention of sorts may be just what she needs to see what she may lose if she doesnt get control of her drinking