My mother - age 90 - has been suffering from stiff hands. She has had therapy and nothing seems to work. She has no control of her hands.

What about some warm gloves? I sometimes have aches in my hands and when I think about it, I put on some gloves and that seems to help.

Warm/hot water softens muscles.
Dishwashers have become both a blessing and a curse.
Ther are little sand filled balloons used for hand therapy. You squeeze them & roll them around in your hand. Works great for stroke victims & also loosens joints/muscles.
That which is not used atrophies and becomes stiff.
Are the joints swollen? Artheritis may be the culprit & not easily treated.
My mother is also 90 & claims her hands "don't work" but you would be amazed at what she can do when no one is looking. Hope this is not the case with yours.