After sending the nice email to the Head, I have had an email telling me that if DD2 doesn't turn up at either the new school or the old school tomorrow, she'll pass on the information to the legal team and I'll be fined.
I've phoned the Inclusion Office and told them the situation. They're going to write a note on the database that I've informed them DD2 has a new school place from Monday and is visiting the school tomorrow, that I have bought uniform and am registered on their 'parentmail' system.
She's really going for me, isn't she?