maggieandme, I totally get where you're coming from. Like you I was a first time pet-owner when we rescued our two 1y old cats, Lucky and Molly, 3.5 years ago.
The two most important things I learned:
Firstly, it has taken them both 3.5 years become comfortable living with us. But they...
I'm so sorry you had that awful experience. Sounds like Meffy definitely didn't like that vet. I have never seen a cat being injected into the thigh - my cats have always been injected into the scruff. It might be worth contacting the vets to discuss.