Elizabeth!
I think you and your 3 year old are going to have a fantastic time! Sounds like you've already got some great stuff planned. Akershus is definitely the best place to meet the princesses. They all walk around and greet you as you eat. Your daughter will be thrilled!
You can also meet some princess for a photo opp at The Judges Tent in Toontown at Magic Kingdom. When you are in Epcot, you will be able to see the princesses in their "homeland" (Belle in France, etc.). You'll also see them in parades and special shows.
Other things for your 3 year old to see? One of my very favorite attractions is Mickey's Philharmagic at Magic Kingdom (a great 3D experience), Kilimanjaro Safari at Animal Kingdom (close up of tons of animals), Journey into Imagination at Epcot (hands on fun) and Playhouse Disney show at Hollywood Studios (awesome show with all your favorite characters).
Also, check out my favorite resource, the
Magical Beginnings Guide which shows some highlights for kids under 5. Enjoy your trip and ask again if you have more questions!