Young Catherine's Black Magic

If I'm not mistaken, Catherine threatened Joseph that she would exercise her black magic on him. Was she being serious about it and what does it say about her religious beliefs? She mentioned something about wax figures of the people and other such things. Also, she was called a "witch" by Lockwood in the book as he narrated the small incident. It seemed like Lockwood thought that Catherine was only saying that jokingly but then I was surprised to see that he called her a witch. I was very confused by all this.