If having problems with depth perception and or precise muscle control unusual for her until late, changes in vision was just the first thing I thought of. It does sound medical though. If you haven't looked into that, I would, and probably before taking keys, though it might be necessary.
We went through it with dad. Wish he had been in your mom's mental condition, but no. Just like granddad, and my uncle on father's side, Alzheimer was kicking in, all three around age 85. Dad waited too late with Grandad when dad was just a little younger than I am now. There was a wreck that almost killed grandmother, and broke granddad's neck. They get brittle with age. The wreck did not kill him, but the rigid cast and halo drilled into his skull locking him down did.
Hate to hear it for you. When the time comes, you will just have to do what you have to do.