Hi Voice Hope your Mother is feeling a little better
the others have offered some very good advice all I can offer is to rest the arm on a pillow and use a heat pad or hot wheat sack ,
i'd suggest going to the local hospital or her local Doctor perhaps they can offer steroid injection or even an increased course of prednisone to get her over the bump.
it can be hard when someone is grouchy when in pain I tend to curl up alone (lucky I'm not grouchy because I'm in a constant Flare of Pain ) But Hubby is the Grouchy sort if he has a cold or in pain and it is Very hard to be nice so I just leave medication or cups of tea for him sort of like leaving food for a grizzly bear