When in December? I was there the week before Christmas a few years ago and we had to wear winter coats. Especially in the evenings. They tell me it was an unusually cold December and then this year it was really cold a few days as well. I think as far as weather is concerned it is a hit or miss thing. We did wear capri's but no shorts. Always had a sweater or light jacket and 3 nights long pants, winter coats and gloves. If you daughter is going to wear princess dresses I would get some long underwear that matches that way she won't have to cover her beautiful dress with a coat. As far as shoes, just make sure they are comfy and make sure you bring more than one pair and switch them out. Each pair of shoes rubs different parts of the foot. By changing them every other day or so you are less likely to develop a blister.
Go to weather.com a few days before you go and print out the 10 forecast for Walt Disney World. It is fairly accurate. Then you can change out any clothing options that might not work. For some strange reason, I think it is the lakes, between October and February EPCOT is always freezing cold at night. Even if it is chilly put your sunscreen on. Kali River Rapids and Splash Mountain will soak you so if you do not want to be wet do not ride them.
Make sure to visit the Monorail resorts for the decorations. The Grand Floridian Gingerbread house is a sight to see. Most important tip-----have fun!