The Orthopedic Foundation for Animals (OFA) gathers information about knees, hips, elbows, thyroid, and other orthopedic ailments. So, yes, OFA reports would be what she means by "testing their hips and knees". FYI, she's probably testing "luxating patellas" when she means testing knees. Just so you don't get confused by the medical jargon.

Honestly, I probably wouldn't contact her vet unless she was really sketchy. If she health tests her dogs and participates with them in sports regularly (i.e. showing them), I don't see a huge benefit in contacting her vet. A vast majority of vets cannot or will not speak negatively about their clients to another person. It's a whole liability and confidentiality thing, so I don't think you'd gain much valuable insight if you did contact her vet. However, you can't really lose anything, so if she happily agrees to let you speak to her vet, go ahead!

Edit: Can I also say I'm absolutely elated that you're being so dedicated to doing it the ethical way? Over the years, I'm sure we all run into folks who don't know how to really check out breeders; we try to give them advice and they usually don't respond. But seeing you respond so heartily really made my day! Kudos!