Hi there I understand your concern... Improper exercise techniques and excessive strain can aggrevate her symptoms...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 ...so I would suggest you to consult nearest orthopedic surgeon they will guide you further including exercise part.