The problem is due to degeneration of knee joints, which is worsened by loss of lubricating fluid inside the joint. All because of vitiation of Vata. If she is overweight, that gives burden on compromised knees and due to pain, patients stops walking / movements, which increases the weight more. Ayurvedic treatment will definitely help to relieve her pain and heal her knees. Along with medicines, Panchakarma such as Janubasti, basti will help a lot. Cap. Gandh tail - twice a day will help ease her movements as it improves the lubrication inside the joint. Consult Ayurvedic physician for proper treatments.
Most probable cause at this age is osteoarthritis... It's a degenerative bone disease...There’s no cure for osteoarthritis as yet, but there are a number of treatments that can help ease symptoms and reduce the chances arthritis becoming worse...options are analgesics, NSAIDs,intraosseous steroid injection and hyaluronic acid injections,Physiotherapy like strengthening exercises etc ... Treatment depends upon the stage...I would suggest you to consult nearest orthopedic surgeon they will do the needful.