A cortisone shot often takes a week or more to have an impact, but if it does, it could mean a few months of relief. Not improvement, but the pain will go. That will give your wife time to plan.
DF just had one this summer at 79, he was bone on bone. It's the kind of thing to do sooner than later - much like investing! - you get more out of it the longer you have your new knee. His scar is amazingly low key too, even at just 3 months after I was surprised. Maybe 4-6 inches but hardly noticeable.
If she is diligent with the rehab, she'll be mostly normal in 3 months, but keep up the activity and strength training as a new normal after that. Walking is nice, but weight bearing stuff is really needed.
(oops I didn't realize this was a 2024 thread lol...)