No matter which meal you choose for CRT, Cinderella will be in the lobby for photos as you enter. For breakfast and lunch, a variety of 4 other princesses will be there. I have been there several times and seen Aurora, Belle (in blue), Snow White and Jasmine each time. Others rotate in occasionally, like Alice or Mary Poppins. Dinner is hosted in the dining room by the fairy godmother. She does a cute (but short) little show where she mentions the special celebrations (birthdays, anniversaries, etc) and dances around the room. Suzy and Perla the mice are there dancing about too. But they don't really stop for pictures and autographs like the princesses do at the other meals. It's a great experience regardless of when you go.
If you're considering a trip to the Bibbidi Bobbidi Boutique on the birthday, then I highly recommend dining later in the day AFTER the makeover, so you can capture her new look in all your princess photos!
We're trying to get there for my daughter's birthday in Sept. The problem with going for a birthday is that you really need the ADR THAT DAY. A day later in your trip just won't be the same. I really hate this new 90 day window thing. At 180 days your odds were really good. I"m not convinced that will be the case at 90 days.
By the way, regardless of what anyone says about the food, it's a great experience. Dining from your table overlooking Fantasyland is unmatched in Disney dining!