I think that your thought process is right. Your not psychic and some Ts might work that day while others don't. plus she didn't say anything about rescheduling until you brought it up. She should've mentioned it earlier on and rescheduled those days in order to avoid issues. Perhaps it slipped her mind because she has a bit going on with her vacation. She should still take a moment to think and be considerate towards her client and address matters appropriately and at a timely mater.