If you have a
scooter at the resort and use Disney transportation, it may be necessary for someone else to park and get it off the bus. The manuevers are tough sometimes to get the scooter parked correctly on the bus; so, it can be locked down properly. Most bus drivers will not help in this matter; There may be a few kind ones, but it's not their job to park the scooter for you. There's a manual overdrive on scooters that some people use to get the scooter in it's proper place on the bus to park it. The resorts are large and it would probably be a good idea to have a scooter there, as well. The price difference is significant between renting at the parks and doing an off site rental for scooters. It's a long trek from the bus stop to the entrance of the parks, too.
You need to charge the battery every night if you have a scooter all the time. You need to get the scooter in her room every day, too. She will probably need help doing these manuevers. Scooters are not wet friendly. If it's raining you need to seek shelter. Many cover the scooter if they are parked for a while. You can a poncho for it.
I strongly suggest practicing on a scooter beforehand. They're free to use in stores like
Walmart, Target and grocery stores. Those scooters are not identical to the ones you will have at Disney, but it's a start. Most people rent the portable, travel scooters which are smaller. You can try those at medical supply stores locally. Try a three wheel one and a four wheel one to see which kind feels better to her.
I would even suggest going to a local zoo one day and using a scooter there for practice. It will be a great way to tell if she can endure it. If she can't do well at the zoo she may have bigger issues at Disney. Disney is a 6 to 12 mile hike for most people. It depends on how long you stay each day. She may need an afternoon rest back at the resort.
Keep in mind the scooter driver has responsibilities, too. It can be challenging driving a scooter through a crowd. People will dart out in front of you and you have to be prepared to stop or manuever the scooter away. One of the hardest places to drive a scooter for us is the Land Pavillon in Future World in Epcot. If you want to do the Soarin' ride you need to take the scooter down an elevator to continue to use it. The Soarin ride has a very long ride queue and it's a popular ride; so, the wait can be long at times. I have used a scooter and my 75 year old husband has used a scooter too many times to mention; so, I have some personal experience, here.
You don't have to go on the rides to have fun at Disney. We go with a 90 year old mother in a wheelchair and we still enjoy the shows, exhibits, parades and fireworks and do very little with the rides. You can transfer to a wheelchair on some rides and then use special ride cars to enjoy the ride. Scooters do not go on rides. The dining can be fun, too; my mom likes the character meals.
I would definitely alternate doing rides with other more restful activities. Don't be a commando with the rides. If possible, maybe you should break away from each other if you find the need to do ride after ride all the time. You can meet up for meals and shows and such at different times of the day. Cell phones do great for catching up with one another. If she's new to Disney then I wouldn't suggest this the first day.
I'm not a doctor, but I know some get pain relief from cortizone shots in the back and some even do accupture for relief there. I would pursue pain avoidance options with her doctor. Also, I would talk with the doctor to see what he/she advises in this case on rides and such. Maybe, she shouldn't go on any rides, right now. If you don't make her feel she will be missing out she can still have a good time at Disney without rides. There's so much street entertainment and people watching for one. Alternate and take turns sitting it out with her and have some great conversations.
You will definitely need a travelling and stadegy plan. Use those EMH times in the morning. The parks will not be as full; so, manuevering the scooter will be easier and you will get on rides quicker. I do think this can still be a good trip for all. Family is what make memories, not rides. Disney for us is the best place to enjoy for someone in a wheelchair or scooter. I will say I'd rather go to Disney with a scooter than not go at all.