This is a great opportunity for your DD to learn to use the broken-record technique for setting a boundary around questions. "Principal x thought Ms. y's room was a better place for me," or something else similarly non-committal (and attributing the decision to those inscrutable adults in charge, not to herself), repeated to each and every question until they stop. The trick is that you don't vary the words or tone at all, so it becomes super boring to keep asking about it. It can be hard to pull off sometimes, but it's very effective.
