As you said, your mother's knee has arthritis and her joints have narrowed, which is caused by years of busy hands and feet and no exercise, and she often has joint pain everywhere. In this case, it is recommended not to do too much exercise at the beginning, and you can use light exercise such as exercise bike instead of spinning bike! That's too much exercise. We should arrange her exercise time according to her physical condition. Don't dare talk nonsense if you don't know the situation!
This kind of exercise bike will do.