A couple of things in the article make it sound like she was trying to pretend that she was one of their classmates -- the official's remark about how it gradually became clear that the messages weren't being sent by a child despite the references makes it sound like the mom was either pretending to be anonymous classmate or impersonating someone. As for why, who knows. Probably trying to break her daughter and the boyfriend up but for what reason there's no way to know.