I was reading a comment where someone wondered whether Mary Shelley wrote Frankenstein? I think I may be able to add fuel to the fire on that question. Mary’s father was a philosopher (William Godwin) of modest reputation. He would have been quite capable of writing Frankenstein. If we assume that he is in fact a ghost author for the book then, this would explain the intellectual maturity and complexity of the story. One of the problems with attributing the story to Mary is that she was too young to have acquired the lexicon used in the narrative. This is why many doubt her authorial claim.
Perhaps William Godwin dictated the story to Mary so as to provide the young lady with a means of income. Back in those days reputation was everything. Poor Mary had family problems so the father may have thought that giving her the story might help her out a little?