First, I think you need to find out if your mom can handle a scooter. You can start out by going to a grocery store and using their store scooters to practice for free. Disney will be much more crowded than any grocery store, but at least you can get a taste of how it is with a scooter. Next, try a local zoo; most have scooter rentals. This will be more true to life as with the Disney parks, but it still will be harder at Disney. It may not be a bad idea for you to try out one, too. This could help you instruct your mom better for it. Some are naturals with a scooter and have no problems using them. It just depends on the person.
None of this practice time will prepare you for the on and off of the scooters and Disney transportation. When we do this with our MIL we get the scooter on and off the buses and so forth for her. We will do the scooter for some of the ride queues for our MIL if they have too many twists and turns. The bigger the scooter the harder this manuevering can be. Also, we will park it for her on some of the shows inside. I do a lot of clearing the path for her; so, we have fewer problems with the crowds. MIL had an annoying habit of adjusting her sun hat all the time or scratching her nose. Anyway, she would use her hand to do it and then the scooter would stop suddenly; because, she removed her hand from the scooter. She did so much of this it was very time consuming and somewhat dangerous stopping so suddenly. By the way, at the time she was still driving a car. You can also go to a local medical store that carries scooters and see how the smaller one would be there. See if you can try out a 4 wheel and 3 wheel there. Most likely, you will rent from the outside source a Pride to go scooter and that model should be available to look at locally someplace. They will let you test drive one probably in their parking lot. These smaller scooters are easier in some ways, but harder in other ways from a bigger scooter. Finally, if your mom has trouble with the scooter there is a responsibility on your end that she doesn't run a kid over or anyone else. She could hurt herself hitting a barrier or whatever. I've seen some strange ocurrences in my time with scooter drivers.
Anyway, we started out renting in the Disney parks for a scooter. When we did it there the price was more reasonable. Then one day, Disney replaced their old scooters with new ones and the price went up too much for my blood. Ever since, we rented outside.
If you park hop as the previous poster mentioned it can be tricky to get the second Disney scooter from another park and again you stand in line. It's a non issue if you stay in the same park. You have to stand in line each day to get a scooter from the park. On the other side, if something goes wrong with a Disney scooter a CM will help and get it replaced for you very quickly. This will not be as easy with an outside source if there is a breakdown. Next, you don't deal with getting the scooter on and off buses, nor do you have to charge the battery up each night, nor do you need to get the scooter in and out of the room if you rent at the parks. If you forget to charge the scooter then you will have to rent one at the park, anyway. Next, you have to consider how you are going to get your mom back and forth to the resort each night without having a scooter all the time. Depending on where you are staying it can be a long haul getting out of the parks and back to a resort without a scooter or a wheelchair. You can bring your own wheelchair to the parks and keep it at the scooter rental each day in the park. Just get a receipt that you are leaving a wheelchair there. If you are driving yourself to the parks this may be a little easier, but then you have to take the scooter apart and place it in and out of the car. If you are doing the car thing at all you can just bring the battery and charger in to get the battery charged up.
One trick I learned about pushing a wheelchair is to alternate activities for a rest. I do many long trips with my mom in a wheelchair and I push: I'm 58 and somewhat overweight myself. I have had tendonitus at times in my elbow, too. Anyway, I will do a ride then a show, then do another ride and another show, then another ride and eat someplace, then another ride and a parade and so forth. By having rest periods I've been able to handle the wheelchair pushing for my mom without having tendonitus again. We don't do long days at the parks; we average 8 to 10 hours per day. I'm stating this in case the scooter idea doesn't work out. My own mother never learned to drive and she has Alzheimer's and there's no way I would ever let her do a scooter. It's not always the best answer.
As I started out to say there are pros and cons to either way. You have to decide what's best for your circumstance.
Your mom may not be willing to do a scooter all day once she tries one out. This is a good reason to test out a local zoo with her and see how she does for a day there. You will have to be very patient with her on a scooter for the first time. You may have to help with the scooter at times. Places like the Living Land (where Soarin' is located) in Epcot is one of the hardest places to do a scooter; it's just too crowded and conjested. You even have to take an elevator with the scooter to do the Soarin' ride there. Believe me, your mom won't be able to walk the Soarin' queue without her scooter.
Finally, scooters have a speed control; however, no rental or park scooter will go that fast. I believe they are designed to go 4 or 5 miles an hour. There's a gage were you can go at tortoise speed or hare speed.
