If it's all said and done there's nothing that's going to change anything. If the "girl" said she didn't want anyone informed I would go along with her wishes.
What if the girl was 12? 11? 10? 9? Where do you draw the line between a mature 13 year old (an oxymoron in my view) and a vulnerable child?
My daughter just turned 11. This kind of story terrifies me.