I'm with CantExplain here - it was my first instinct to wonder why your T didn't relay the special privileges/concession (as if it should even be one in the first place) to the receptionist. How else did she think it would be accomplished?

I also don't think you should have to put yourself through the worry of trying to explain the situation more emphatically to your T. It sounds to me like you spelled it out pretty clearly and tactfully for her - why should she wait until you're kicking and screaming to help you out with it? Furthermore, what the hell is wrong with these people that they make this blanket policy and penalize all patients for the flakiness of some? Are they running an elementary school or what?

The receptionists have absolutely no excuse for being rude to you - customer service is their effing job. If they don't like it, they can go be dishwashers or bill counters for bookies. (Or get some therapy of their own.)