Sorry to be asking an obvious question, but if other keys do work for movement and she isn't likely to have developed muscle memory for WASD, why not use alternate keys? Also, do the arrow keys work as expected for movement? Mouse?

I'm not suggesting giving up entirely, and I understand wanting to solve the mystery and being worried that other, yet unseen but potentially related, issues may pop up down the road. That said, alternate movement keys might be best for now so she doesn't tire of the tech issues and can dive into the game to see if it's for her. Just an opinion on possible option, you of course know your mum best.