My grandmother was living alone and driving around for years. Then it seemed she got into a few fender benders in the space of a few months, nothing serious but sort of thoughtless. It was soon after that we took the keys and moved her in with us. It was really difficult. She felt like she was being caged up, forced to give up her freedom, and could be searing with words.
It was the right call, she was diagnosed with alzheimers soon after, but it was tough for her to make the change, and accordingly tough on us too.