As everyone else has said, Disney on wheels is really easy. I'm a wheelchair user and find that WDW is one of the few places that doesn't make me 'feel disabled'. Just a few random thoughts from me:
Make sure you don't hurt yourself! If you need a break, take one! Also, if lifting her into ride cars is difficult, some rides have wheelchair accessible cars where she could stay in the chair. These take longer to come around (there's usually only one in circulation), but they may save you some stress and pain.
On the buses, you might want to consider having her stay in the chair to ride. The driver will strap her and the chair in place, so no need to worry about her rolling anywhere, and it will make it easier to protect her leg from being jostled and bumped by other passengers. It also means you're not trying to hold onto a couple of over-tired three year olds AND a wheelchair!
For your ADRs, it might be worth just phoning ahead to say that someone in your party will be using a wheelchair. That way, if that restaurant does have any steps, they'll make sure to put you somewhere accessible.
One fun thing that I always do is to decorate the wheelchair. This always gets us compliments and strikes up conversations, and it may make her feel less self-conscious (if that's an issue). Could you get characters to autograph her cast, if she's still in it by then?
Make use of the wheelchair viewing areas for parades and so on. It will mean she'll still be able to see everything and you won't have to worry about some numpty standing in front of her at the last minute (yup, this happens!). It should also reduce the risk of her being bumped and jostled.
If she ends up with swelling or in pain and needs a break, the first aid centres will let you use one of their beds to put her foot up for a bit.
As someone else said, the tops of your legs and feet are much more exposed in a wheelchair than walking, so make sure to keep putting on the suncream.
Have an amazing trip!
