From the sparse information provided, the pupil walked out at the end of the first exam and went home.
This isn't the case. He didn't go home. He knew he had another exam in the afternoon, it didn't realise it was a clash exam that others sat earlier in the day.
He left the hall, returning in time for the exam and at that point he was challenged about leaving the hall where he should have remained.
His medical issues would have meant he needed to leave the room anyway (toilet and to walk around) though this would have had to be supervised.
Apparently the school clash rules state that if a student leaves the room, it's an automatic disqualification.
She asked me for help as he may get disqualified, because I mentioned how my Dsis has recently helped 2 of her friends win appeals for school entry places, but this situation isn't quite the same.
I did ask my Dsis who isn't a teacher and she said it is a shared responsibility between student and the school..... but the school is responsible for ensuring adequate supervision in these situations in accordance with JQC or JCQ.
My colleague has an appointment with the HT tomorrow, so I'll let her know what's been said here.
Thanks for your responses.