We were just at the Grotto last week, so a word of advice: I'm not sure if our crowds were typical or not, but we learned REAL quickly that lines build up for Ariel fairly fast. She didn't arrive in the morning until 9:30, but waiting the 25 minutes or so until she came was nothing compared to the near hour-long waits we witnessed for the rest of the day. Every time we passed the sign, it read anywhere between 50 and 70 minutes to meet Ariel. It'll definitely be worth it for your DD, but my advice is to get there early, even if you have to wait a little while for her to arrive.