My mom got lost for 6 hours driving. She has the early stage of dementia. How to take her car away?

I found the only way to totally convince my mom was to tell her doctor that she was getting lost while driving. When her doctor put it in writing that she was not to drive she did not. She was perhaps ready to give it up a little before that when one day she got to the corner of her street and had no idea which way to turn to drive to my house. She reported it to me, which I thought was an admission. Another day she stopped at my house to ask directions to the bank. I drove her.