Does she have specific princesses she wants to meet? We took our daughter at that age (she's 6 now) and frankly of all of the princess experiences we have had/paid for, the Grotto was the worst value. haha. It was nice to knock out 4 in one go, but you can do that with planning yourself.
-the top tier of the bibbibi bobbidi boutique makeover used to include an escort to the front of the line at the royal hall, where you'd meet 3 princesses. I have heard it doesn't include the meet and greet anymore, but you may want to check if that's something you/your daughter might be interested in. It's like $199, comes with the full makeover and dress.
-if you check the app the day before you go, it gives you a rough idea of when/where princesses are meeting you can make a general plan. On one day of a 4 day trip, I spent 3 hours and my daughter met like 8 princesses. For example, Aurora met at 9:15 at the wishing well, with Ariel coming at 9:45. Got in line to meet Aurora at 9:05 so we were the first ones. Went and did something for 20 minutes, got back in line around 9:30 so that by the time we were at the front of the line again, Ariel would be up. CM's will usually be helpful with this if you're waiting to see a specific one. Trucked over to meet Belle or whoever at Fantasy Faire at 10 (got in line at 9:50.) Immediately went over to meet Jasmine who met at 10:15. Went to NOS to meet Tiana at 10:45. etc etc etc. My point is, you can seriously minimize wait in line if you get in line early.
In my experience Anna/Elsa is consistently 20-30 minutes even on the slowest of days (or we just have bad luck?) and there's no getting around it unless you go there first thing maybe? Like a PP said, it's a nice wait in the animation building anyway. And, if one of you is waiting there, she can always go for a 10 minute walk or whatever. Anna and Elsa were new and still in DL when my daughter was 3, and I totally had to wait in line for 2.5 hours outside while my daughter took a nap in the stroller somewhere else and woke up right as it was time to go in. ha.
Also FWIW the line for the royal hall is especially short at the beginning of the day, or during/right after the afternoon parade.