Patrish,
Call me contentious, , or whatever, but consider McGrath's advice--I have found that if you feel anger about something like this that doesn't go away, and have fantasies about getting even, litigation is the best revenge.
Make a few calls to file the appropriate complaints, get your ducks in a row, get introduced to a few people at the local papers and sketch out your story, and then, when you go to the "do", you can be pleasant for the whole evening, and on your departure, you may smile sweetly at the headmistress and say, "It's not over."