Though Green's book The Leavenworth Case is frequently cited as the first mystery written by an American woman, The Dead Letter by Seeley Regester was published earlier (1866).

[2] In a discussion of women writers of detective fiction, scholar Ellen Higgins in 1994 chronicled the work of Green as popularizing the genre a decade before Arthur Conan Doyle brought out his first Sherlock Holmes story.

Indeed, as journalist Kathy Hickman writes, Green "stamped the mystery genre with the distinctive features that would influence writers from Agatha Christie and Conan Doyle to contemporary authors of suspenseful "whodunits".

In addition to creating elderly spinster and young female sleuths, Green's innovative plot devices included dead bodies in libraries, newspaper clippings as "clews", the coroner's inquest, and expert witnesses.

[6] Green was in some ways a progressive woman for her time—succeeding in a genre dominated by male writers—but she did not approve of many of her feminist contemporaries, and she was opposed to women's suffrage.