If she's that convinced that her doctors are right, I don't know whether my 'success story' would help, but here goes.
I'll be 70 next week, but I began developing osteoarthritis in my mid-30s, and was headed for knee replacements as soon as I was "old enough" (in those days, they only lasted about 10-15 years and doctors wanted you to be at least 50). I took NSAIDs for inflammation for years before I learned better. Over time, the effects of the osteo were throughout my body (my podiatrist once told me I had the 'worst' foot he'd ever seen from arthritic degeneration).
In my 50s, I began eating low carb and doing water exercise. Gradually I realized that the NSAIDs didn't make that much difference. With diet and exercise, I got off all meds (although my doctor told me that would be 'impossible'), and when I consulted a surgeon at a major hospital about replacing my knees recently, he told me to delay as long as possible since I'm controlling the pain so well on my own.
Grains and sugar are the killers--if I have either, I have pain within hours, so it's easy for me to avoid both. As a measure of my success in controlling inflammation, I had a CRP test a while back (measure inflammation in the body), and with a lab range of (1.0-12.0), my number was 0.9--below the lowest.
At 70, the only Rx I take are for my Hashimoto's (hypothyroid), and I feel more fit and healthy than when in my 30s.