Check the Disney Magical Experience App for times. The schedule is to see her at Epcot is typically 12:30, 1:30, 2:30, 4:20, 5:20 & 6:20pm.
The Epcot characters sometimes have weird times, so be sure to check it on the day you're there.
She's also at Akershus and Cinderella's Royal Table. There's also the Disney Princess Tea Party at the Grand Floridian if she's between 3-9, but that's also really expensive.