If it would work for you, you may want to consider modifying your reservation to include a Preferred Room at Pop Century. By doing this, you will be able to have a room in the 60s building that will place you closest to the main building (where the food court is). However, there is an additional charge for this room, but you'd have the peace of mind knowing you have a room that would be beneficial for your mom.
If that isn't a possibility, I would make a notation in your reservation that explains your concerns. Then when you arrive and check-in, again remind the cast member of your concerns. While they can't guarantee anything, I'm certain they will do their best to help your mom out. The 60s building is the closest building while some rooms in the 50s and 70s would also place you nearby.
If you have a free moment, make sure and stop to look at all the memorabilia in the cases at the resort; I thought it was fascinating to see the collection of icons from each of the centuries!