Agree with the rest…you've probably done what her family were unable to bring themselves to do…remove her from the road!
Had a similar situation myself last month, was following a utilities van along an A road in the dark one morning, every time a vehicle approached coming the other way the driver would stand on the brakes and slow from approx 55mph to 30mph and then speed up again. I had a huge distance and was still catching up each time and the cars behind were getting irate. Once we got to a dual carriageway, the cars overtook us both (I was in a van so let them go first) as the first pulled back in a few car lengths in front of the van the driver braked and almost stood the van on its nose, luckily I'd already pulled out and I shot past. Driver did the same everytime someone pulled in front of him for the next five miles or so until he pulled off.
Was going to report him to the company as driver was either drunk from the night before, on drugs or needed a serious eye test. But then I started wondering if perhaps, although he was middle aged, he was a new driver and inexperienced etc etc, could lose job etc if not fit to drive, etc etc and chickened out. Still not sure if it was the right decision…