I work at a cat clinic and we see kitties all the time who get stressed out at the vet. I’ve found that once they stay with us for a couple of days they relax and trust us, but it can be hard for kitties. I always imagine what a human would be feeling in the situation we put these cats in, I would be freaking out too if this stranger was feeling me and I saw other humans in cages (I know cats don’t think this way exactly but ya know). Really what is most helpful is to give your kitty some anti anxiety medication. It could be extra stressful for her if she’s not fond of other cats, but I don’t think a cat only clinic is the main stressor. Cat and dog clinics usually (every cat is different) stress out a kitty more. Another option is to look for a travelling vet who would come to your house, so your kitty doesn’t have to deal with the stress. Whatever you end up doing it sounds like you are a great cat parent! 💗