I have a similar issue with my mom, only she's on all sorts of heavy duty pills (highly likely addicted to pain killers and other prescriptions). I live 700 miles away and she absolutely refuses to move to assisted living. 

I don't think her driving is that bad, but doubt if she should be driving. I've called adult protective services and they told me that until she starts a fire, crashes the car, or completely disables herself, there's nothing they can do. So I've just given up. And discussion of her pills just gets my head bitten off. So I go there 4 times a year to help some (which is always miserable for me) and wait for her inevitable disaster (medical emergency, overdose, etc.).