I think what we have here is: " a failure to communicate"... line from a famous movie....now who said that? Umph can't for the life of me remember
I think first and foremost on the dog owner's part. When she changed the spay/neuter and cleaning appt, just to a dental. If I was worried about my pup sitting for a long time in a clinic waiting for what-ever procedure, I would ask the doc's office, okay do I still bring him in at 8am? How long will the procedure take? Will he be ready to go at noon? Earlier/later?
I know that we don't always think of questions "we should have asked" prior to dropping our pet off for a procedure; but on the other hand some pre-printed information sheets a vet's office can and probably should have should cover some basic FAQ's with respect to commonly performed procedures of that clinic. The client is handed the appropriate info sheet, and then can read it and refer to it, before, during, and after the event.
I don't think this vet's office did anything so egregious, and if the quality of their healthcare is good, I'd just spend a moment or three to rethink my position. Then calmly determine, what I want to have happen differently the next time; and go about insuring that a) I communicate my wishes to the appropriate clinic official and b) re-iterate that communication prior to "dropping off my dog" for the next procedure I have done.