On my past couple of trips, I had only seen the Princesses at MK and EPCOT. I hear that some will appear at MGM by the Hat in the afternoon as well.
World Showcase at EPCOT is the very best place to meet Princesses in WDW. The lines are often shorter than the ones you'll find at MK plus World Showcase makes such a beautiful backdrop for the pictures. On my last trip, Mulan was in China, Snow White was in Germany, Jasmine was in Morocco, and Belle, Aurora, and Cinderella were in France. All were pretty easy to find off the main promendade except for Mulan who was back near the shop in China and Cinderella who was in the garden in the back of France by the perfume shop.
Toontown is also a nice spot to find the Princesses, but be sure to get there early since lines get really long. Usually Cinderella, Snow White, and Aurora are there with sometimes other princesses taking their place if a regular can't make it. I believe Cinderella is always there though. If you miss a Princess at World Showcase, or if your daughter just wants more princess time, definatly check this location out. Along with Toontown, there's a few other locations at MK where Princesses show up. Jasmine usually hangs out near the Magic Carpets in Adventureland, and Ariel is always at her Grotto unless the weather is too cold (in which case she appears at Toontown). Aurora is now doing meet-and-greets after the Let's Have a Ball show behind the castle, and Belle does a meet-and-greet after her storytime. I believe both of those meet-and-greets are limited to people who see the show before it. Also, sometimes Princesses show up in Town Square.
Esmerlada doesn't seem to be making appearences lately. If she's even out, I would guess she would be at the Hat at MGM, France at EPCOT, or perhaps some random location like the Toontown or something.