Do you keep the cat carrier tucked away since you don’t use it very often? “Yes” is the wrong answer. The carrier is triggering for a lot of cats. They associate it with going to the vet’s office, which they hate to do.
Thus, the right thing is not to hide it so they only have to get upset once in a while. It’s to leave it in plain sight with the door open and to put some toys and treats in there from time to time so your cat will view it as a comfy place to hang out. Line the carrier with a soft towel, perhaps switching it out with a fresh one from the dryer every so often, and she will enjoy it all the more. Then, when it’s time to go to the vet, she won’t feel so freaked out.
