@Utwenzel - as
@SueM in MN said, the *average* Guest walks between 5 & 10 miles PER DAY at WDW.
As others above have said, most likely you will be told that this is a mobility-related issue that is resolved (in Disney's mind) with either the rental of a wheelchair or an ECV.
And as
@gap2368 said - rent offsite if your trip is for any length of time beyond about 3 days; you will save money
If you rent a wheelchair, you need to be prepared to push her; even a highly conditioned athlete in top form cannot sit down in a wheelchair and self-propel around WDW without pre-training. She might make it one day, but will be in bad shape following that, with shoulder, arm, hand and possibly even back issues.
An ECV is most often recommended because most users can sit down and drive with little to no training or practice. ECV's can go almost everywhere at WDW; the few places they can't (the
smaller launches to/from Poly, GF, WL & FW - the larger boats to/from WL & FW are still accessible - and a few ride queues) you can ask any Cast Member what to do, and they will assist you. All of the boats (with the exceptions noted above), the Monorail, and all buses are ECV accessible. Additionally, with the new Minnie Van service, there are ECV friendly Minnie Vans now as well ($20/ride anywhere on property, up to 6 people).
With a couple of notable exceptions, all of the Resorts at WDW are huge, and you can easily walk 15 minutes just to get coffee in the morning. With an ECV, she will have the freedom to come and go as she pleases at the Resort, as well as at Disney Springs, which has nearly doubled in size over the last couple of years.
There is ample room to park an ECV inside every Disney Resort room - just make sure to completely recharge it every night.
Knee walkers are notoriously difficult at WDW; if she is healing, and wants to walk about, she can always park the ECV anywhere in the Parks (if you are unsure, ask a CM, and they will show you a safe place to park out of the way) and then walk around an area, and come back to the ECV to ride for a bit when she gets tired.
The ECV is just a tool for her to use - like the knee walker - to accomplish an objective: have the best possible time at Disney World!