The "Belle Greene" in question may be Isabel Colton Greene of Nashua, NH who is documented in the online Union Catalog of Letters as corresponding with Clemens. The letters database is online at: http://www.marktwainproject.org This "Belle Greene" is Isabel Colton Greene (b. 1842 - d. 1926) who was a writer. Clemens owned at least one of her novels _A New England Conscience_. Her spouse was Martin Van Buren Greene of NH. There is a photo and biographical profile online of her in google books in _A Woman of the Century_ by Frances Elizabeth Willard, p. 337. Barb