From the New York City Public Library collection via Wikipedia; flaws in background fixed with Photoshop by gogm.
"Lingerie dresses" were in style and Countess Dudley appears to be wearing an example under a robe edged with sawtooth lace trim. Her bodice looks like it could be part of a corset.
Keywords: Countess Georgina of Dudley, Moncreiffe family, Ward family, Countess, British, curly coiffure, scoop neckline, modesty piece, long sleeves, coat, collar, lace, choker necklace, necklace, earrings