((((des))) I'm sorry you're experiencing this. If you can continue, without expecting any thanks, then do so... but take care of yourself first. I agree that she might be going through ppd. If you can suggest to her to get some help (MD or whomever) that she needs a break or ??? do so....

But again, take a break; it sounds like you need one to for all you've been doing for her and the family. ((((hugs))))

And to answer your subject line question: I hope not. Anger only eats ourselves up inside, does nothing good for a situation. We here at PC appreciate you, who you are, and what you have been trying to do for your sister.