We Have An 11 Year Old Female Bichon. Despite Her

We have an 11 year old female bichon. Despite her age she has always acted like a puppy until about a month ago when she gained weight unexpectedly and started shaking from time to time. She sometimes seems to have trouble with her paws which have become very tight. The vet is treating her for arthritis but not for the shaking. We are very worried about her.