Doctor refusing to inform the DMV that Mom has dementia that impairs her driving! I quoted from info gotten off the internet that Medical Report Form must be completed by the Doctor if their ability to drive is impaired. I was told they would not do this without my Mother signing a consent form first. Well duh! If Mom would be willing to sign that, then why would I need anyone with official legal authority to do this for me in the first place?
I would send the form in a certified letter to the doctor, specifying that your mom has been diagnosed with dementia and asking her/him to sign the form. You CC it, also certified to DMV.
Alternatively, you could ask the doctor to send her for a driving evaluation. If she fails, those folks ( they are usually OTs) will notify DMV.
If you have a teaching hospital nearby ( one that is affiliated with a medical school), call them and ask to speak to someone in that department for a referral.
We had a guy close by us who drove off the road into a field, got disoriented and froze to death over night. One old guy got 'on' at the 'off' ramp and had a head- on collision that was fatal for him. God forbid your relative injures someone else, runs over a child, gets lost in the wrong section of town, runs off a strange road into a ditch or onto the railroad tracks, etc. You are going to have to be the one to deal with it.