I'm curious as to how you got your total average transport times - I'm guessing you figured how many times you'd like to go to each park, looked up the transportation times from someplace like the Unofficial Guide, and added up based on each resort?
And does this include the approximate time you'll spend waiting for buses, or just time actually on a bus or ferry or monorail in transit?
And is a car an option? With your mom's condition, you could probably get temporary handicapped stickers or plates and park close to each park's entrance?
Regardless, I'd be leery of Kidani unless they could specifically accommodate your need for a room close to transportation or the parking lot. Saratoga and Old Key West might be your best bets because they have multiple bus stops so wherever your room is, you have a fighting chance of being close to one. They also are the biggest DVC resorts and for various reasons aren't as popular, so that improves your chances of being close to a bus stop. And the condo shape of BLT might improve your chances of less of a walk once you're IN the BLT building; whether you're close to the ground floor or all the way up top, if they can accommodate the request "close to elevator," then it wouldn't matter what floor you're on as long as you were a few steps away from your room once you arrive on your floor. The downside there is the bus stops are at the Contemporary, so you'll still have to at least walk to/from there.
EDIT: Also, not for nothing, but I'd humbly suggest changing the title of the thread to something like "Best DVC resort for mobility issues" or something like that. Because while your mom is a "noob," I suspect making things easier for her might wind up being more important to your decision that overall awesomeness. Case in point, most people here want to die and be buried in Wilderness Lodge for all the Disney Magic it screams, yet for completely understandable reasons you don't even consider it an option.