Oh I feel for you and her, that is a tough one. It is better she gets evaluated though, for her own safety and others, unfortunately I don't think there's a win-win to be had here.

I don't know financial circumstances but maybe if she does have to stop driving she could use the money from car sale and saved from insurance/tax etc, to fund an account with a local taxi firm? Might be less of an affront to her independent spirit to get a cab than a senior bus if she can afford it?