Speaking as a 15y teacher, this is a horrifying situation, and something that could have EASILY happened to any teacher I know.
She was seriously let down by her school and the school trust, whose initial actions were not to support her, but to throw her under the bus. A long-standing, respected senior teacher, with a previously unblemished record.
The parent is a piece of trash, but I'd like to hope that as the boy grows up, and hopefully enters the world of work himself, he realises - and is sorry for - the role he played.