i remember going to support groups when my teenagers were using drugs and one of the first things that we were taught was when we make a decision concerning boundaries.....there is no discussion of it with the teen. if you allow a tiny crack to show in your armor, then it's gloves off and you find yourself mired in a sea of "what ifs", "oh yeahs", "why nots", etc. etc. etc....i imagine your sister is pretty good at manipulating the entire family and if you give her the opportunity to make you "discuss" your boundaries..it's hell to pay!! good luck....pat