Most people...not all people..use dogs who are bred for hunting due to characteristics you might want.ie Pointing, fetching, prey drive, good nose. I have heard of people using non hunting breeds and doing just fine. It all Depends on the dog.
You can teach older dogs..but just like people. The older you get the harder it is to learn. “You can’t teach old dogs new tricks.” Make sense? I am sure you can teach an older dog. But a young dog is a lot for adept to learning.
The dog regardless of breed needs to have the hunting instinct and drive embedded in its DNA. Like a human that “just isn’t in to it” a dog is the same. That’s why hunting dogs are bread from parents who are hunters themselves. It’s the only way to positively pass on that trait. However, some dogs who are mutts have a little hunting passion in them that is somewhere in their DNA and can be taught, but it’s partially natural. We had a short little dog growing up that was a pure mutt, but that little bastard used to fetch dove like a world champion. Besides my dad feeding him a cold Budlight, the dog would fetch the birds on his own. He was definitely an exception to the rule.
Take her out in the field and see what she does. The biggest issue with older dogs is dealing with them being gun shy. Take her to play in an area around a skeet range. There is a good book called “Gun Dog” I think. It would be good reading material for you. Good luck!
Thanks for all the info! Will be trying all of those things. Do the dogs usually help with multiple kinds of upland game? Or do you focus your dog on one type of bird? I'm looking to hunt quail, dove, and attempt to hunt pheasant and chukar.