From personal experience I can tell you forced never works. In my opinion you can tell the SIL your feelings. Let her know that you will not be there for her when she is drinking. Detach with love from the situation. She will have to decide that she wants a better life. I would be interested in knowing what your brothers role is. An interesting read is Pernell's Addictive Personality post, if you have time. Please keep posting and reading here because her drinking is apparently affecting your life. I'm sure there will be more knowledgable replies than mine.