No, I don't think you are being unreasonable at all. The prevailing thought amongst the more progressive vet community is that older dogs don't need any further vaccinations, beyond what may be required by law (rabies). A similar thing happened to me a couple of years ago, when I had to use a walk-in clinic to get a rabies vaccination for a trip to the U.S. (our regular vet was fully booked, and this was last-minute). I only realized after I left that they had also vaccinated (via a second syringe) for distemper/parvo etc. I wasn't paying too much attention when they were vaccinating him, and hadn't really processed the fact that they had used 2 needles.
According to Dr. Jean Dodds, however, vaccinating senior dogs seems to be troublesome only if the dog is experiencing geriatric-type disorders, or has a problem with the immune system. I would think that if your dog is fairly robust, healthwise, that she will not suffer any ill effects. If she is still frolicking at the dog park, it sounds like she is doing well.