Who is going to take responsibility for the car accident? Doctors, police, certainly not the dementia patients.

I just need to vent! My almost 86 yr old mother was told by her 1st neurologist that she is no longer able to drive to drive. (Diagnosed 8 months ago with Dementia) After 7 months she decides she IS going to drve. 1st Neuro. told her that if she feels that she can drive, she will need to be evaluated at a cost to her of $252.00. She does not have that kind of money to waste. But she did take the test. She had a GOOD day the day that she took the test. Low and behold, the instructor told me she did very well on the driving test, I stated that she was having a good day, he said that her Neuro. would have to make the "final decision" but he didn't see any reason why she couldn't drive, as long as she doesn't drive whenshe is having a bad day. I explained that was the problem, she doesn't use good judgement and it wouldn't make any difference to her, as bull headed as she is if she decides that she is going to drive, she is going to drive. Even if she is "mentally lost" that day. And again all I got was she just needs to use good judgement. In the mean time, we make appt. for the neuro to give her the driving results. Due to circumstances beyond our control, the 1st Neuro. tells us he can not accept any Humana patients until April , 2012. So we call and make an appt with a 2nd(different) neurologist. We go today, and to our surprise, guess what??? The Doctor tells us that from her scores, and because she is having a "good" day today, he can't do anything about it and she CAN drive!!! My sister and I both protested and told him she has had 2 very close calls to a head on collision, that she runs over curbs all the time, that she drives too fast and sees nothing but what is directly in front of her. My sister asked "so if she gets into an accident, it is your responsibility then and it will not be ours because we are telling you that she should NOT be driving, is that correct?" He says "NO, it will be the responsibility of the people that gave her the test, because they are te ones that passed her".
My Mother is in very good shape, physically. Very active and wants to go, go, go. Mentally, for the last 2 weeks she has been a total mess. As anyone with knowledge of Dementia, you now it's a "roller coaster" ride. Day to day.
What in the world are these doctors, physical therapists and evaluators of driving tests thinking??? I live with my parents 5 days a week, and my other 2 sisters are there on weekends BECAUSE she can't take care of herself, let alone my father (he was diagnosed 4 yrs ago with dementia) . Would you not want to get information on what the patient who is with them 24/7 is doing on bad days? Or ask them what the bad days are like? Her mental status on those days? They have just given her permission to go out and kill someone. And there is not a thing we can do about it. The dementia is making my sweet, totally caring, loving mother, someone I do not know. She is sneaky, she lies about things and puts on such a good show when she has to. AND THE DOCTORS DO NOT SEE IT!! I just can not say how upset I am. Any advice from anyone????? Takin the keys or disabling the car will not work. As I said. She will call for a locksmith to get new keys. My father is a terrific mechanic, by trade, so disabling the car will not work. All 4 of us kids have pleaded to her not to drive any longer, her sister and brother also stated that they would not get into a car with her ever again after a close call with them in the car.
I just d not know where to go from here. We have done all we can. No one will listen. It is a shame that all the calling out for help goes on deaf ears.
Thank you for letting me vent. It didn't help much, but I am looking forward to any suggestions anyone has. THANK YOU!