Oh Joe, I know the agony of trying to stop a parent from driving when they become dangerous to themselves and others. I'll be sending you some good vibes that all goes well with your mom.
When my Dad got Dementia he crashed into a 'car club' of 9 classic Volkswagons that were stopped on a Freeway off ramp. He just failed to stop causing a chain reaction tail to front collision of all of them.
He didn't report the accident to DMV and lost his license, his insurance paid (thank goodness) but then cancelled his car insurance. Despite all this, he continued to drive.
We took his keys but he found others somewhere. Finally I told him he wasn't safe to drive and would cause injuries and damage. His reply was, "I don't care, I don't care if I kill them all". At that point, I knew my Dad wasn't in there anymore and we took the car so he couldn't get at it.
My mom, on the other hand, surprised us all by voluntarily giving us her keys when she knew she wasn't good to drive. Saved us a lot of heartache.
Hang in there with your mom, be vigilant and hopefully she will realize you are right. I'll be praying for all of you.