From eBay. According to the seller's caption, she was Lady Constance Gertrude née Leveson-Gower, wife of Hugh Grosvenor, who was created Duke of Westminster on 27 February 1874.
Blemishes in the background and her neck and the corners were fixed with Photoshop and the sepia tone removed by gogm.
The Duchess' full skirt shows this photo was taken before 1875 when skirts became very close. Her modiste relied on scalloping for decoration and, on her bodice, saw teeth.
Keywords: Duchess, Sutherland family, Grosvenor family, British, braided coiffure, chemisette, high neckline, long tight sleeves, jacket bodice, collar, buttons, long close sleeves, cuffs, full skirt, ruffles