So sorry about your aunt and the denial by the son. The denial part is almost as maddening as the disease.
I am familiar with the problem about driving. Either go on line to your state-site or go to the DMV. They will have a form for you to fill out for re-evaluation for driver's license. I down-loaded the form and filled it out about my FIL. It is anonymous! You do have to sign your name, but they don't know who or why they get a notice for re-evaluation. My FIL thought the insurance company turned him in because of all the accidents. (Not only does FIL have AD, but epilepsy!)
On the form, it will ask for either birth date or driver's license number. It also asks for reasons you think they should be re-evaluated. I made a list of every incident I could think of and health issues. I was notified by mail that they received the information and about a week later, he got a notice in the mail. In his letter it gave him a time and date to go to the DMV for an appointment about re-evaluation. He thought he would just have to take a test there, but they suspended his license and gave him forms for his doctors to fill out.
That's why in your case it will be really important to have documentation of the problems she has while driving....(and while living...) Make sure you mention her son is in denial and write down every AD incident you can think of. Mine was rather easy to document as FIL has so many health and mental issues. Road rage, accidents, getting lost, etc. plus his AD, seizures, heart problems, optic nerve swelling, etc. etc.
Even if her doctor is in denial, he will have to list all her medications and will be held liable if he says she is capable of driving. Your aunt will in the least have to be re-tested. (She may not even give the papers to her doctor.)
They gave my FIL a book to study. (He is suspended for 6 mos. because of seizures.) Of course, that hasn't kept him from behind the wheel. My next course of action is to go to the local police. They know him and would have to pull him over if they saw him driving. He has to drive right by the police dept. to visit his brother. (MIL has no control over him due to his rages and her heart condition. It has always been a volatile relationship which is exacerbated by his AD.)
I haven't had to worry about him driving lately as he hasn't been feeling well. He's retaining fluid and his legs and feet are swollen. That's the only reason he's not driving....he can't walk out to the truck.
If his problem clears up, I will have to go to the police about his suspension.
So start by going on-line to find out the name of the form you need. Good luck to you and God bless!