DDog has been diagnosed with luxating patellae
The most important protective things you can do is keep the dog the right weight and keep her active, though you need to avoid lots of stairs, jumping up on things (fat chance for the sofa! But train out as much as you can) and lots of steep hills - if unavoidable where you live, go gently at the dogs preferred pace not your own walking pace.
I'd always say go with vet advice about whether and when to operate - especially when you're getting a second opinion from a centre of excellence.
Physiotherapy is another option, but I don't know what difference it wouid make at grade 3.
DDog was still an older puppy when it was first spotted, and was on watchful wait with grade 1 on one side and grade 2 on the other. It never popped spontaneously (just when she wobbled on the edge of a raised bed, jumped down off balance and landed badly). So we were very careful with her weight an exercise. She was still growing, and the joints are much more secure now - clear on one side and nearly clear on the other - can still be moved on manipulation by the vet, but with difficulty. If she hadn't been diagnosed before, she probably wouldn't meet the threshold for diagnosis either side now.
So yes they can improve. But aim off - she was never x-rayed so we don't know if there was a skeletal issue (groove too shallow, and I think that can only be improved by surgery) or if it was loose muscle/connective tissue which has stabilised as she finished growing. I don't even know if that's biologically possible!!
Hope all goes well at the appointment today. It's always worse when the patient is a family member who can't explain understand what's going, and who it's impossible to explain to!