OMG Hun, massive question to be answered re arm. Sounds like they been rough with her when lifting her up the bed or something. I would get a posse together and camp out 24 hours, take it in turns. tell em you are there to keep an eye on nan and watch that she eats. sounds like they being abusive, cos that is surely what it is.
My Nan went though something similar in the care home, but it was a woman who was supposed to be doing for her and she used to torment my Nan. I hope you get answers hun, I really do.
Hugs xxxxx