Hi Jeffery and wife!
4 years old is certainly a great time to take your daughter. I've always thought 4-7 is the best time for children, because they're old enough to understand where they are, and still in that phase where everything fun feels magical! And who can do "magical" better than Disney right? :-)
I took my daughter 2 years ago when she was 4. We certainly went the "princess" route for her, which she absolutely loved. Here are some things that were memorable for her:
Bibbidi Bobbidi Boutique-set a reservation at the Boutique to get your daughter glamorized! We took our daughter at 4, and it was easily one of her top experiences! If she has a favorite princess, I'd buy a princess dress and shoes off-site, then bring it with you to the Boutique. My daughter dressed as Belle that year...
On the topic of princesses, take her to Cinderella's Royal Table at Cinderella's Castle for breakfast, where she'll get to see (and meet) Cinderella, Jasmine, Aurora, and Snow White. If not the Royal Table, take her to Akershus in Epcot (Norway), another enjoyable princess experience. Of course, it's cheaper to eat here under a Dining Plan than paying out of pocket, so if you can fit it in your budget, get the Basic Dining Plan at minimum.
The Kilimanjaro Safari (Animal Kingdom) was a big highlight. If your daughter likes animals take her here! The Kidcot Fun Stops at the World Showcase at Epcot (crafts) are fun.
Smaller things my daughter enjoyed was the monorail. Even if you don't stay at a monorail resort, find a reason to get on. This was a big deal for my daughter at 4.
And water: Whichever resort you stay at, take her to the pool! Most of Disney pools are heated (we took our daughter Christmas week that year) and she loved it.
There are so many others but this will quickly turn into an essay :-) Hope this helps! Enjoy!