You got a lot of really good hints already. I'll just explain a little about the GAC that SueOKW mentioned.
It stands for Guest Assistance Card and is a way to quickly tell CMs what sort of assistance you might need (besides just having things be wheelchair accessible). Things like, a quiet place to wait out of crowds, a place to wait out of the sun, etc. You can request a GAC at Guest Assistance at any of the parks. The card will be valid at any of the parks for the entire length of your stay and is usually issued for the person with a disability plus up to 5 memebrs of their party.
If your child needs to rest for a while, First Aid is great. They have little cubicles with a cot, a chair and a table. A lot easier than going all the way back to your resort if you just need a little recharging.
A 6 year old is still small enough to take out of her wheelchair to put her on rides and hold her. Enjoy that while you can - she will get big soon enough. One other thing, for most of the rides that have moving walkways to get on, the CMs can slow or even stop the ride. The exception is Peter Pan - that one can't be stopped.