The school claimed it was for their protection, but resorting to such manners is still morally wrong in my view.
As for kinky conversations, the best bet really is to keep them out of school. Every year, I sign a document saying "I will not access pornographic, sexually arousing material etc." and I'm sure some would argue that this counts as a breach of such a policy (if it is in place). If it was not happening in school (again, I don't know if it was) the school are (I'm sure) not allowed to use her username and password to access her account. And if they are, it is wrong.
As for kinky conversations, the best bet really is to keep them out of school. Every year, I sign a document saying "I will not access pornographic, sexually arousing material etc." and I'm sure some would argue that this counts as a breach of such a policy (if it is in place). If it was not happening in school (again, I don't know if it was) the school are (I'm sure) not allowed to use her username and password to access her account. And if they are, it is wrong.