Dear DIvya,
It seems that your mother is having age related joint changes, which includes pain, stiffness, degenerative changes & reduced joint space in Xray. Changes cant be reversed but symptoms can subsided and strength can be maintained to avoid surgery.
ask your mother to do prescribed exercises for the knee pain regularly, it would help her in long term.
Next Steps
visit a good physiotherapy centre where they will give you pain releiving modalities and some exercises
Health Tips
avoid complete knee bending and stairs climbing