It might be good to give her a chance to practice with an
ECV before you go. A lot of larger stores, such as
Walmart and Target have courtesy
ECVs for customers. They are apparently a lot heavier and harder to drive than those from the off-site rental, so if she can drive those, she can drive anything.
It might be best to talk to her about it before you go. I've heard a few people on here say that they rented an ECV for someone without telling them, and they got pretty upset about it and refused to use it. Don't let something like this spoil your trip.
One trick that often works with people is to pick a place about two or three miles away from her home. Then ask her if she could walk all the way there. If she says she could, ask her if she could walk there and back again, every day, for the length of your trip. She'll most likely look at you as if you're mad, but four to six miles is actually a fairly short distance to clock up in a day at WDW.
Also, explain to her that, though you want to do everything you can to make the holiday fun for her, you just can't cope with pushing a wheelchair all the way around Disney in the August heat. Make sure she is aware that the ECV will offer her more independence, and help her to have fun without getting tired or being in pain. If she is someone who likes to feel 'useful' you could say that with the ECV she could go ahead of you to pick up fastpasses, or help you guys with the bags (a lot of ECVs have a basket in the front).
Do you know what her concerns are? Is it that she doesn't like the idea of driving it, or is worried she might hit someone? If this is the case, a few 'practice runs' around Target, and a few turns around your resort when you get there should help her to feel more confident. She might also be happier if you did EPCOT on your first day, as it has wider paths and fewer crowds.
If her worry is slowing you guys down, just assure her that she will be able to go a lot faster and stay in the parks much longer if she saves her strength for the fun stuff.
If her worry is the cost, tell her that it's a small amount compared to the entire holiday, and it will mean you can
all enjoy yourselves more!
Hope some of this is a help!
