Just got back from WDW. We took our almost 3 year old DD and 4 year old DS. We took our own stroller and rented one in Epcot on the day we weren't staying late. Since our kids are on the big side, our stroller can be hard to push and the rentals seem to move better.
I would definitely bring your own. There are plenty of places to park your stroller - you will see signs for Stroller Parking. We have never had our stroller taken. I will alert you that CM's are often moving strollers within the stroller parking areas to make them fit better, so you might want to tie a scarf, balloon or bandana to your stroller to make it easier to find.
My DD loves the princesses, the Peter Pan ride, and It's a Small World. We rode that a lot! She was scared of the Pooh ride for some reason, and also liked the carousel, Dumbo and the Magic Carpets.
I packed a couple juice boxes and some snacks in my backpack each day. DD likes peanut butter crackers and Teddy Grahams. Neither are messy and both take awhile to eat since there are individual pieces, so they keep her busy when in line or when we needed her to be settled.
DD loved Storytime with Belle in MK. It's along a walkway between the castle and Tomorrowland that goes along the teacups. Belle comes out and tells her story and kids get to be in the show if Belle asks and they want to do it. Afterward, those who watched the show get their picture with Belle. Much of the area is shaded and you sit on benches, so it's a nice break. It takes about 15 minutes. We did it on a day without Spectro and Wishes so the park wasn't crowded, and we walked in and got a second row seat about 7 minutes before the show.
We also had to stop and watch Cinderellabration many times because DD loved it. It's short and doesn't take up much time.
If you're not sure how your daughter will do with characters, don't schedule any character meals the first or second day. My DD starts off shy and then after a couple days, she's hugging all of them.
A mid day break is nice for kids that age - even if she won't nap, try a dip in the pool. The parks are so visually stimulating, a break helps prevent tantrums.
My kids loved
MNSSHP. My advice because of your DD's age is not to waste time trick or treating that much. The lines were very long because of the way it's set up, and since your DD probably won't be staying at the party until midnight, just wait till you're leaving the park and then you can fill her TOT bag from a bin on the way out. The longest lines were on the walkway between Toontown and Tomorrowland and by the Jungle Cruise. Get your free family picture early so DD's in a good mood. Spend some time on Main Street so she can see the ghosts projected on the buildings. Princess Jasmine and Aladdin are behind the Magic Carpets ride if DD wants her picture with them.
Hope this helps. Have a great trip.