Mary Shelley is the famous author of the Frankenstein series of books and a former acquaintance of the Styne Family.
Mary was an acquaintance of the House of Frankenstein and was presumably trusted by them as they allowed her to spend a few nights at Castle Frankenstein. During that time, Mary learned of the Frankenstein family's secrets. Horrified by the family's actions, Mary wrote the novel Frankenstein as a way of going public. Mary's actions forced the Frankenstein family underground and they eventually became known as the Styne Family. However, no one believed Mary's story to be real.
In Dark Dynasty, after being captured by hunter Dean Winchester, Eldon Frankenstein revealed that the Styne Family were originally known as the House of Frankenstein before Mary Shelley wrote her book. Dean expresses doubt about Eldon's story, questioning why Mary didn't go public if its true. Eldon points out that Mary wrote a book and "you don't get more public than that," a truth that Dean acknowledged.