Our most recent visit was quick 2 park day trip in January. My daughter was a day away from turning 4, my son was 2.5.
We did MK and Epcot. Epcot is great for a princess fan with the Frozen Ever After ride and all the princess meets around World Showcase (Anna & Elsa in Norway, Belle in her blue dress/white apron in France, Mulan in China, Jasmine in Morocco, Snow White in Germany.)
The princess meal at Akershus is also great (we always do a late breakfast).
My kids love Epcot. If your daughter is 40” tall, she’d be tall enough for Soarin’ and Test Track. For attractions without a height restriction, my kids love Imagination, the Seas with Nemo and Friends, Gran Fiesta Tour, Frozen Ever After, Turtle Talk, Spaceship Earth and the Land. We love AK but can spend much more time with the kids in Epcot than at AK. There’s a ton of stuff to do. They get a kick out of the jumping fountains and love playing in the area after Journey into Imagination.
When I was a kid, my parents used to give me a little money to spend as we walked around World Showcase. The shops in China and Japan are so fun. We’re going to start doing this with our kids next year. I collected so many cool things from the different countries as I was growing up.
The kids also low exploring the countries - the garden maze in the UK, trains in Germany, waterfall in Canada ... just so much to see!
My vote is definitely MK and Epcot!