"My wife was in a car accident – hit from behind – some time ago that has left her incredibly uncomfortable/nervous as a passenger (with anyone driving, including myself). Taking Ativan or equivalent is not a solution. Can you suggest any cannabis-based solutions – with reasonably fast onset – for her to try?"
Your wife should look into tinctures and sublinguals, as well as portable vaporizer pens. This will give her the fastest onset of relief. If she cannot tolerate THC, you can also try CBD-dominant products, which will have less psychoactivity but still provide relaxing and calming effects.
CBD rich tinctures and sprays are awesome for anxiety and can be discreetly used which is always a nice thing. Plus a modest dose won’t have her incapacitated, but she should find relief. There’s a lot of companies making high CBD products with a bit of THC in them
I agree with the other with both answers. Sublingual tincture or CBD dominate edibles, and quite possibly paired with some simple peppermint and local honey.