I know how hard it is to break, because I do it to myself as you know, we are much harder on ourselves than we are on others.

I kind of figured your family was very repressed. Your sister's response is seriously F'ed up. You are struggling trying to "obey" and then alternately " rebel" against that programming from childhood, and you feel somehow that you are defective - it's NOT you who has the problem, it's them. You are experiencing normal emotions, just to an abnormal extent because of PTSD. You shouldn't feel ashamed of not adhering to a seriously F'ed up rule.