She married twice, but produced no children. Her mother is not known. Her article in thepeerage is here.
From the museum's Web site.
This drop dead gorgeous beauty is the half-sister of Marguerite, Countess of Blessington. She wears her hair straight with a tasteful chignon behind.
Keywords: 1840, Landseer, Ellen Power, Nelly Power, Viscountess Canterbury, straight coiffure, vee décolletage, modesty piece, elbow length close sleeves, cuffs, ruffles, full skirt, necklace, bracelets