For your mother ergometric or upper body exercises are best. Please see a PMR doctor who is into diabetes
foot related speciality. NOT A PODIATRIST PLEASE. If you do not have any physical medicine rehabilitation
specialist, then make sure she moves her upper and lower arms while sitting on a chair, while lying on a back. A lot of muscular exercise is possible eventhough a person does not walk. This can not only help her for diabetes but for cardiovascular risk reduction also.
Get back to me for any further related query/ guidance.