She's not in the theater, but she typically meets in that dress at the flag pole in MK at the very start of the day. Only for the first hour or so, though, and then she switches out with Stitch (previously Marie).
Epcot Character Spot would be the most reliable place to find her, and you can use FP+ there, too, if so desired. (It's worth the FP+ for now since there are so few in Tier 2 that need the pass - we'll see what changes happen once Soarin' and the new Frozen offerings open, though.)