I understand your situation now.Quite honestly I see no reason why you would be in any trouble.  You were acting in good faith here.  The girl said that she couldn't go home and you didn't want to strand her at a school that was closed.  Finally, when you got home you immediately informed the police as to her whereabouts.  If anything you acted with due diligence.If the facts are as you say, you deserve to be applauded.  Some people would have not gotten involved and left the girl.If someone is threatening some kind of legal action I don't think that they have a leg to stand on.Hope this  helps.