Oh just another thought.

Have the vet that did the dentistry confirm in writing that he said the second rabies shot in under six months will not have any adverse effect on your cat and tell him you will be taking legal action against his practice and his veterinary licence if anything happens to Rosie.

If he won't do it, well, there's your answer. If he didn't read her records and see that she had just been vaccinated, the phrase professional negligence springs to my mind.

I wouldn't let this rest, and I certainly wouldn't be paying him. If you scare him enough he might think twice before being so handy with the needle next time.