Doc Intrepid, I have the complete Sherlock Holmes at my place, and to my recollection, when Holmes carried, he carried a Colt revolver.
Watson had his Army revolver, which is what it was usually called in the stories, but I am not sure if Conan Doyle ever specified Enfield or Webley.
Edit: +1 on a 1917 in Colt or S&W flavor, unless she's looking for a carry pistol - I have a Colt 1917, and its concealment poses challenges. For a carry pistol, why not a Colt 1903 .32acp? Or a 1908 .380? Those are pushing into early Edwardian, but still should meet Goth/Steampunk criteria.
Second Edit: Had to fix the "correction" made by my spell-checker. Irritating...