I'm really happy to report that Dr. Sherman at VetHab found no physical concerns in his examination of Lucy. He said that she is in great shape for a 10-year-old dog. So I still don't know why she was refusing the teeter, but I feel a huge sense of relief that it's probably not physical. (She didn't refuse the teeter a single time this weekend, leading me to believe that it's something about unfamiliar teeters she doesn't trust). I will continue to limit her runs and still plan to move her to Performance after her ADCH (I already enter her in NADAC Veteran's class), but at least I know that she's sound enough to stay in Championship until I manage to get those last two Gamblers Qs.
Dr. Sherman did tell me I need to expand my pre-run warm-up routine to include a few minutes of walk/trot/canter/gallop in addition to the stuff I already do, and I need to make sure I do it no more than ten minutes before a run. I've already been feeding Lucy joint supplements for years (glucosamine/chondroitin, MSM, fish oil and vitamin E), and he said to keep it up. In reference to Pinky, I asked him at what age he recommends starting a pup on supplements and he said 4 years or after the first incident/problem.
He also told me that if Lucy has another bout of "mystery lameness" like she had a couple months ago to call him immediately and they will fit us in as soon as possible.