Hey there, Kyle!
On one of our recent trips to Disney, my husband needed to use an ECV and renting one was so easy!
Each Walt Disney World Resort theme park offers
ECV rental at the entrance gates for $50 per day with a $20 refundable deposit. If you will be park hopping, you will need to return the ECV to the rental location, receive the $20 refundable deposit and present your receipt at the next park to show that you have already paid the $50 fee for the day. Don't forget, you must also pay the $20 refundable deposit.
If your mom will need an ECV for the entire trip, including at your resort hotel, there are local, private companies that have delivery service and multi-day rental option.
Here's a list of those private companies.
Best Price Scooters and Strollers
Apple Scooter
ScooterBug
CARE Scooter Rentals
Buena Vista Scooter Rentals
I hope this helps to make your family's upcoming Disney vacation even more special for your mother!
Happy planning!
Korliss