Your mother seems to be having osteoarthritis. Osteoarthritis is a type of arthritis that is caused by the breakdown and eventual loss of the cartilage of one or more joints. Cartilage is a protein substance that serves as a "cushion" between the bones of the joints. Osteoarthritis is also known as degenerative arthritis.
Treatment includes reduction of weight, exercise and support devices like splints, canes, walkers, and braces.Non steroidal anti inflammatory drugs like ibuprofen are used for pain relief. Some studies, but not all, have suggested that the food supplements glucosamine and chondroitin can relieve symptoms of pain and stiffness for some persons with osteoarthritis.Intra-articular injections of cortisone are also helpful in relieving pain.
For persisting pain of severe osteoarthritis of the knee that does not respond to weight reduction, exercise or medications, a series of injections of hyaluronic acid (Synvisc, Hyalgan) into the joint can sometimes be helpful, especially if surgery is not being considered.
Surgery is generally reserved for those patients with osteoarthritis that is particularly severe and unresponsive to the conservative treatments.You can take a second opinion from other orthopedician/joint specialist regarding total joint replacement.
Hope it helps.Take care and pls do keep me posted if you have any additional queries.