Christie's has this about the portrait: "STANISLAW MARSZALKIEWICZ (POLISH, 1789-1872)Princess Golitsyna, in white dress with frilled collar and sleeves, smocked bodice, seated in red velvet chair leaning on her right elbow, her dark hair upswept; landscape and sky background.
signed 'Marszalkiewicz' (lower left)
rectangular, 5½ x 4 5/8 in. (140 x 117 mm.), gilt-metal mount."
I darkened the image somewhat to bring out details of the folds of her dress.
In checking this image, I verified Golitsyn and Galitzine are indeed different spellings for the same family's name.