I had a friend who was that defensive. When I finally confronted her, after quite an eventful night that ended with me and a security guard dragging her out of a bar and pouring her into a cab (she was our designated driver that night, too!) She didn't speak to me for 4 years.
But for me - I had to shed myself of a toxic relationship for my own sanity. So I was ok with the no contact.
This is your sister, so its a little different. I can't offer any suggestions, because as long as she is living a life that is working just fine, she has no reason to really look at her drinking habits. I would instead gently suggest working on your own detachment from her drinking.