Just a hunch, but I've seen CMs go up to people and ask about doing special things, and I think there are some things they are looking for, including a little girl between 5-9 (just in that size/age range from a glance) in a group that is soaking up the magic as they enter the park in the morning, without another girl in the same range with her.
So often I read about the families that get picked to be grand marshals and it happens to folks smiling and enjoying just being at the MK, not racing to be the first in line with a character on Main Street, or running to get to Space Mountain first, or generally frowning, fussing, or arguing as they pass by.
I know the parade family is approached in the first hour the park is open, on Main Street, and I'd bet that's the case for the lucky little princess, too.
Here's hoping a DISer gets to enjoy and come back and report!