Yes she has. J.K. Rowling actaully sent off some her own sketches along with a sample of her first Harry Potter book to a number of agents and publishers. She has also revealed a selection of early sketches on her official website, including a scene from the first book and a number of character sketches (one of Hogwarts ghost Nearly-Headless-Nick, Peeves the Poltergeist and Hogwarts Sorting Hat). Rowling released the sketches as a reward to fans for discovering special hidden content on her website.
Rowling also produced a number of sketches for her companion books, Fantastic Beasts and Where To Find Them and Quidditch through the Ages. These two books contain detailed sketches of creatures and Quidditch equipment.
Rowling has also showed some of her artwork in a number of interviews, and produced a map for the filmmakers to use as reference for the design of Hogwarts and its surroundings.
Rowling also produced a number of sketches for her companion books, Fantastic Beasts and Where To Find Them and Quidditch through the Ages. These two books contain detailed sketches of creatures and Quidditch equipment.
Rowling has also showed some of her artwork in a number of interviews, and produced a map for the filmmakers to use as reference for the design of Hogwarts and its surroundings.