I am glad that someone was standing there and saw the receptionist being ugly. I know that you are nice and try to deal with it yourself but when people do that they need to be reported or it will happen again, to you and/or to others if they get away with it.
I would like to think that if you (and others) had reported just the facts every time the supervisor at the hospital that they would have gotten a clue as to what was going on sooner and I would hope that they would have done something to/with her to make the situation better. Hearing it as people were leaving made it look as if it wasn't so bad and people were just looking for an excuse to leave. Same with the other supervisor. Stop taking crap from people. Everyone has a bad day now and then but they shouldn't take it out on people.