In the veterinary practice guidelines at http://www.op.nysed.gov/prof/vetmed/vetpg5.htm, it says New York State licensed veterinarians should:

5.8
decide what medical or surgical cases to accept in professional practice; once you accept a patient, you should determine what course of treatment will be followed in consultation with the client;

5.9
advise the client regarding any treatment to be provided to the patient without using undue influence


Note that these are guidelines only, and they do not carry the force of law.


So it is true that the veterinarian should have advised you that the vaccine might be given; however, the veterinarian assumes responsibility for making medical judgments regarding the health of the patient with the assent of the owner (see paragraph 5.11 of the guidelines).  If the vet performed a timely examination of the cat and determined it was healthy enough to vaccinate, and if the vaccination was therapeutically indicated as part of continuing care and treatment, then that is within the guidelines (as long as you signed some sort of "permission to treat" form giving the veterinarian permission to make medical judgments regarding the cat's health).