I wouldn't necessarily recommend it if she was a lot older, but at 5 years of age, your kitty has a lot of potentially very good years ahead of her. The knee may not seem to be bothering her much for now, but as she ages, I would think it would be likely to get worse, instead of better. And the older she is, and the worse the knee gets, the riskier the surgery would be, and the harder it would probably be to get ideal results. Fixing this knee now sounds like it would be a good investment in giving her a pain free future. If you have the ability to pay for it (and it sounds like you do), i see no reason not to go for it.
Checking out different doctors first sounds like a good idea, and as you talk to them, they can give you much more informed opinions about the likely outcome of surgery as well as the potential results of not doing it. I'd be interested to hear what they have to say. But knowing what I know about aging joints in humans from firsthand experience, things like that do not tend to get better on their own!
Funny story: I had a cat (Logan) who was diagnosed with two loose kneecaps at a routine checkup when he was about 2 years old. The vet said there was no rush to do anything about it as long he didn't seem to be having any problems, but that he might need surgery eventually. As time went on, though, he never showed any signs of knee problems. He finally died of kidney failure at the ripe old age of 17 without ever needing to have anything done about his knees. We never would have even known there was anything different about his knees if that vet hadn't told us about it,
Your kitty's situation is obviously a lot different from Logan's, and she's lucky to have such caring humans who are in a position to get her whatever treatment she needs. I hope you'll keep us posted as things progress with checking out surgeons and making a decision, not to mention the surgery itself, if she has it.