A couple of other suggestions -
The speed control is the most important thing to know about. It will be a lever or knob and will be marked to show the maximum speed for that setting. Most of the time it will be a rabbit for faster and turtle for slower.
The biggest problem my family has seen in the parks is people traveling at too high a speed, so be sure you know where turtle is and use it when she needs more control.
Another important control to know about is freewheel. This allows you to put the
ECV into a setting where it can be pushed and will not be powered. That is helpful if you get into a situation that she can't out of. It's also helpful to know how to put it back in because CM's often put it into freewheel to move it while you were in an attraction. If you find it doesn't work when you come out it may be that they didn't correctly get it back into gear.
Before leaving your resort, make sure she is very confident in backing, going forward, stopping and turning both going forward and backward. The more comfortable she is doing those things the easier it will be for her.
Even though she is the driver, she does not have to be the one to put the ECV I am the bus. Someone else in your party can drive it on if they feel more comfortable, or you can put it into three wheel and push it on. Just be sure it's back in gear before being tied down on the bus.
Anytime she is stopped for more than a short time, it should be turned off. That will not only save the battery, but will also help prevent accidental movement.
The last hint I have is that not all parks are as easy to maneuver in as others. Most people find Magic Kingdom is the hardest because it is small spaces, lots of people and lots of children. So that might not be the best park to start in.
Epcot seems to be the easiest part for most people because there are less small children and the walkways are much wider.