Feral Kitten, limp legs heavy breathing?

Take the kitten to a veterinarian pronto or you will lose her. Not for nothing, the SPCA also has veterinarians! The Humane Society in our area has a low cost veterinary service. It could be illness or it could be an injury but I don't think you should let her suffer. In our township, if you are feeding a cat or kitten you are responsible for it.