I know I'm a bit late to respond however I just wanted to add my vote for the Beach Club villas. SAB is amazing and with the zero entry section, sandy bottom pools and sandy areas to build sand castles, it makes for a great sensory experience and is better in terms of accessibility (not sure if your daughter is one to fully submerse herself in the water so the zero entry option is great - I don't think OKW has that option but I could be wrong). Of course, you will have the kitchen and laundry facilities if staying at a villa and while it may not be as large as the OKW villas, I imagine there would still be enough room for an inflatable mattress. With respect to transportation, you would probably want to avoid the buses but keep in mind that if you have park hopper passes, you can walk through Epcot and board the monorail to the Magic Kingdom. Some people think it's a bit of a hike but we actually enjoyed the trip (it probably took us about 45 minutes from the door of our villa to the entrance to Magic Kingdom). Also, being able to walk to the entrance of Epcot within mere minutes was great and we also walked to MGM (maybe a 20-min walk and very peaceful). We managed to avoid all buses and the only time that we drove was to go to Downtown Disney. As for fireworks, even if you don't get a great view from your room, you can walk down to the beach or to the bridge that connects BC and BW and get a decent view of the fireworks. I was surprised at how much we enjoyed the location. We went in early May this year and the resort wasn't very busy at all. It seemed that SAB was only really busy on the weekends and even then, we would go after 4:00 and it wasn't busy at all.
Sorry if I'm complicating matters but we really did enjoy the convenience of the location especially given the transportation issues.