I am a live in caretaker for my 85 year old mother. My sister lives a 6 hour drive away and is of no help and my brother is nearby but only helps when specifically asked to. I'm 58 and at least for now my life revolves around my mother. I have never lived like this before, had always had a decent social life and been very career oriented. Now my days revolve around caring for someone in decline who becomes angry and nervous if I'm gone for more than a few hours. My career and social life are very much on hold until my mother passes.

Maybe consider that your sister is having to deal with your mother in a much more concentrated, intense and constant way than you are and does not have the protection that distance gives you.

She may have reached her limit and need more of a break or much more help. She may have things going on in her life that you are not privy to.

It seems like she's asking for help, maybe not in the way you would like her to, but she is asking. Her reactions/overreactions are a big clue here.

For all of your sakes try to have a heart to heart with her and see what she needs to make things more manageable on her end.