Suggest Treatment For Severe Ankle Pain While Having Osteoarthritis

my elderly mother-75-has a severely mis-formed ankle that is causing her a lot of pain. It looks as if the entire ankle has collapsed and now when she stands, her instep is closer to the ground than the outter part of her sole/foot. So the inside of her ankle is actually an inch or more closer to the ground than it should be and is bearing most of her weight. She has osteoarthritis and is obese. Recently she suffered a Pulmonary Embolism from DVT in the same leg--huge clot was in the thigh. She has been on long-term steroids for COPD. Can this be fixed? Her doctor prescribed physio and orthotics. Is that enough? What can a physio do about a collapsed joint?? Shouldn t she have surgery or a cast to correct it? I am trying to convince her to get help but she thinks there is no hope.