there is no way to check hours afterwards (and it was far more likely days afterwards) if someone actually had a seizure. You cannot show this on a brain scan. If someone was plugged in during a seizure you'd see brain waves changing, but you can't go into hospital the day after and prove that someone had a seizure.
But the way the justice system works, you can't prove that she didn't have a seizure either. I hope she is telling the truth and actually had a seizure, but it would be possible with good legal advice to say after the fact you don't remember what happened and it must have been a seizure.
They say there has been an extensive investigation, so I hope they carefully checked her phone records to see if her phone had any sort of activity at the time of the accident. I assume this was done. I wonder - given the victims' lawyers are disappointed with the decision - if they have any further information on what was and wasn't checked during the investigation.
If she indeed had an unexpected seizure, of course she shouldn' be charged. Equally, as others have said I am sure the guilt and social stigma that comes along with this is severe punishment already.
I feel heartbroken for the families, it's absolutely tragic.