@raynbow- Using hand exercise ball workouts is a great way to help ward off the stiffness of arthritis in the hands. One of the keys to dealing with any type of arthritis is staying active, and using hand exercise balls helps keep hands moving and strengthens muscles.
You should tell your grandmother to start out slowly, using small, soft exercise balls at first. Show her how to do several repetitions of squeezing them with each hand, then letting go. As her hands begin to feel better, she may want to consider trying larger exercise balls that have firmer tension to build more strength.