This must have been awful for the parents, but I'm with Ms Piggy, it certainly wasn't a deliberate act. Having worked in academic administration, I know that it will most likely have been a mail merge that had an electronic signature (therefore the deputy head won't have signed it himself) and could even have been put into envelopes by a machine, meaning no one would have picked up on it.

I'm sure the people resonsible are mortified, but that will be of no consolation to her poor parents.