Fast Reaction Time + Proper Conditioned Response = No Accident
So what would need to be done is to modify her conditioned responses. It seems like she has conditioned herself to address any danger on the road by braking. The only way I know of to change a conditioned response without actually practicing is to mentally rehearse different scenarios.
Good luck with that. It’s been my experience that people, but women especially, but women you’re dating even more-so, do not take well to driving criticism. I’d just make sure she drives something with a lot of stars under the crash test category.