Helen Vaughan (later Mrs. Herbert/Mrs. Beaumont) was the child of Mary, a mad woman and … something else. Mary was mad as the result of a surgical experiment that allowed (forced?) her mind to see and experience “the Great God Pan” i.e. the vast realms of reality of which the human senses are not aware.
Helen is the focus of the story The Great God Pan by Arthur Machen but the reader only meets her second hand through accounts that one character tells another. She seems to be evil and have the ability to drive men to suicide but the details of her evil and why the men actually kill themselves is left to the reader’s imagination. The story’s protagonists take it upon themselves to convince to hang herself but whether she does so or whether the protagonists kill her themselves is never stated. The story suggests that she hung herself but, to me, that seems unlikely. Why would she?
Helen is a fascinating character, all the more so because the reader learns so little about her. I rather surprised that no one has written an expansion/sequel/prequel of The Great God Pan from her point of view.