No No No No...Your sister doesn't get to tell you how to feel, or what not to address. If this argument feels like it is still unsettled from your side then you have every right to defend your position. Sounds like your sister is quite happy to permit you to remain the scapegoat...No No No. There can be no harmony or moving forward unless this conflict is aired and put to bed. If your family/sister aren't willing to hash this out, then if it were me I would scape them off and move on.