Its only a defence. If she has no history of diagnosable attacks.

I am no expert on epilepsy . But know young diagnosis is far from exclusive. So it is entirly possible this was her first attack. Or even the first attack she recognised as such. (IE not happening when she was asleep or otherwise unable to identify).

But if she has ever had an event she should suspect makes her unfit to drive. She is required to tell the DVLA and not drive.

But that recognition requirement is hard to define. Drivers are not expected to be medical experts. So in general unless a doc has told her. It would be hard to proove she is aware of any risk.

T1d myself. Diagnosed long before I was able to drive. I now do not drive because my condition is not safe to do so. But was in the situation for almost 30 years. Where I was required to testify my stability to drive every few years. And could be held responsible if I did so falsely.