My cats tail seems to be limp,how can i tell if she has dislocated it or broken it?
If the tail is limp and swollen there is something wrong, either infection, which may open up and drain, or like you suggested a dislocated or broken tail. I would think that the vet would have noticed if this was the case if there was a thorough exam done. Even without x-rays these types of tail injuries are usually pretty obvious. Cats are infamous for getting bite wound infections, from other cats, assuming that your cat has opportunity to be in contact with other felines. If it is an infection it should start getting better from the antibiotics very soon. If the problem continues, bite the bullet, and go back to the vet. Better safe, than sorry.