First of all, my Mom was a Special Ed teacher - God Bless you!!!
Your daughter is an amazing kid - I bet because of all of the love and support you have given her, she's going to grow up to be an amazing woman as well!
It sounds like you and your daughter are pretty close. Our BabyBunny was a "Shriner's Kid" from birth to age 18, so she and I developed a very special and close relationship on all of those Hospital trips that continues to this day.
Mom to Mom, here's what I would tell your sweet girl if I were in your shoes:
"Of all the people in the world, I KNOW you don't want to use that stinkin' wheelchair. I KNOW you prefer to walk. But let's use that wheelchair like a tool - just like when you see someone using glasses to see better? They are using those glasses as a TOOL. If you see someone using hearing aids, they are using them as a TOOL to hear better. And if you have to use that chair at DisneyLand? It's just a TOOL for us to go and have fun, and be able to stay and play all day!!! We can get some fun ribbons, bandanas, maybe even some Dollar Store beads, and decorate the chair, and have fun with it! And when you don't need it, we can still just push it around until you need a place to sit! It will just be like a rolling chair we bring along for when you need to sit - you don't have to stay in it all day!
I just want you to have the best day that we can at DisneyLand, and I don't want you to wake up the next morning, in pain. So, our plan is to try for the DAS, but be ready to decorate a rental chair, and go have fun!"
This was - still is - the hardest thing for our BabyBunny. She wants to go go go, and she wants to be as "normal" as is possible. Fortunately, as she has gotten older, it's been easier for her to accept that Normal is just a setting on the washing machine... and that it's OK to be "different", and to even celebrate what makes you different and unique... even if that means decorating your wheelchair or ECV.
I hope you all have the best possible time at DL. (((hugs)))