My older sister does this to me. The only answer I found was to seperate myself from her. I do not go to family functions that she will be at, and I do not discuss the issue with others (family members). If they bring it up I state plain and simple that I choose not to ruin the affair for me and others by being near her negativity. It does hurt not to be able to go to these functions but I figure its better than causing a scene at the function and ending up hurting more than feelings IYKWIM.