God bless your Mom for continuing despite the pain!
Has your Mom seen a rheumatologist? If not, then that is the first step to getting help.
I have a prescription gel called Voltaren gel. It is an nsaid, so should always be used sparingly, especially by someone who is 87! Having said that, it works fairly well.
I have friends who use the wax baths for their hands and swear by them. That might be a good place for your Mom to start. You can get the wax baths in any price range your want, from low to high, but the concept is the same no matter which one you get.
Good luck!