My mothers doctor doesn't recommend that she be driving. Does that make it illegal if she does?

If her vision is impaired to the point she's a danger to herself and others, public transportation is the way to go. Share your concerns with her, everyone who cares about her, the local police, and DMV. If the latter doesn't suspend the license until the cataracts are taken care of, then it's on them if she mows someone down. In the meantime, cover your a__ by keeping everything documented. Someone out there might try to pin it on you.

Just having a Dr say that a person shouldn't be driving doesn't make it illegal. They can certainly write a recommendation that the senior should not drive, however, it's usually up to a family member to follow through and work with the licensing division of the state they live in to have the senior's license revoked.

If the senior is in their right mind, and chooses to drive, it can be quite a challenge for family member's to "take the keys". Good Luck!

I'm not sure what country you live in but in Canada a Dr. can certainly have influence over whether a person's licence gets renewed. Perhaps call the motor vehicle licencing branch and have a conversation with them about what the Dr. said?