I was reading something recently and it said when we are dealing with another person who fruatrates us, has troubles in their life, its always good to step back and try to see from their perspective. It was said to be a sign of personal growth when we can so this. Your comment of how she may be thinking she set boundaries is something to think about. Based on what you described, she has had much to deal with . And you have too. Its a dreadful situation what your going thru with your parents and sister. I hope you can find some peace as you deal with all of it.