Hi Tracie,
Bringing your young daughter to Walt Disney World when she has just turned 3 years old will be so much fun! What a wonderful trip you are planning.
I suggest that you go with the Royal Rooms at
Disney's Port Orleans Resort - Riverside for a couple of reasons. That resort is simply beautiful. It is so lush and lovely. I had a chance to tour the Royal Rooms, and they are absolutely charming. Your daughter will probably love seeing all of the princess touches in the room! From Disney's Port Orleans Resort - Riverside, you do have the option of taking a boat to Downtown Disney, which can be really fun. From a practical perspective, the room at Disney's Port Orleans Resort - Riverside are slightly larger than those at Disney's Pop Century Resort. The extra space might make you a bit more comfortable and able to spread out.
Disney's Pop Century Resort is very fun and whimsical, and is also a great option. The Royal Room at Disney's Port Orleans Resort will be somewhat more expensive than a room at Disney's Pop Century Resort; however, since you mentioned that price is not prohibitive, I think that it is worth it to pay a little more for the Royal Room at Disney's Port Orleans Resort - Riverside.
I hope that this helps with your decision, Tracie. Have a great time planning your trip, and please do not hesitate to ask if you have any further questions.