Her genealogical sketch is here.
From Wikimedia.
The skirt suggests this is from the earlier 1820s when skirts became more rigid. I cannot tell if she wears a necklace at her neckline.
Keywords: Marina Dmitrievna Gureva, Naryshkin family, Guriev family, Countess, Russian, mistress, Alexander I, curly coiffure, jeweled turban, puffed cloth ornaments, partlet, scoop neckline, long close tapered sleeves, tight cuffs, bracelets, laced Empire bodice, square décolletage, strap sleeves, clasps, jeweled waist band, A-line skirt, wrap