1825 Princess Dietrichstein? by Josef Eduard Teltscher (location unknown to gogm)
There is a thread about the family in the Alexander Palace Time Machine Discussion Forum. This person is probably Alexandrine Dietrichstein, née Shuvalova.
Princess Dietrichstein wears a dress that looks forward with the natural waistline and material rising and flaring up and out from the waist band.
Keywords: 1825, Teltscher, Shuvalov family, curly coiffure, veil, off shoulder straight neckline, modesty piece, puffed sleeves, waist band, full skirt, necklace