I wonder if there is a law in the UK that would allow the parents of the boy to sue the mother of the girl for snitching. Like, she weaponized the laws of another country that criminalize behaviours that are legal in the UK, for things that happened between UK citizens abroad. That sounds like something UK legislators might have the power and incentive to legislate, right?
Also, I would not fault the girl if she hated her horrible mother for the rest of her life.