It is a key case because if she did have a fit, and is subsequently found guilty of manslaughter etc it may have implications for those who have a heart attack or similar at the wheel and sadly kill people as a result.
I don’t think that it will have any new implications. I think it has always been the case that in circumstances where a driver suffers a sudden, genuinely unforeseen episode - a seizure or heart attack, say - and this leads to the injury or death of others, then the driver may not necessarily be held criminally responsible. If, however, they had ignored medical advice or knew or suspected that they weren’t fit to drive, then they may be found guilty of a criminal offence. I presume that the police now have evidence in this case to that effect. In the case of the woman in Bristol who was found guilty, it was reported that:
The court was told Fiona Hodge had suffered a number of "weird" episodes linked to undiagnosed epilepsy before the crash.