She was born English and married French not long after the Napoléonic wars were over in 1830. Her husband's Wikipedia article is here. Her article in thepeerage is here.
The imbecile sleeves (?) and ferroniere head band suggest this dates to the mid-1830s. The lace on her sleeves suggest her dress could also have flared sleeves.
Keywords: Dubufe - Claude Marie, Marie Eleonor Jenkinson, Jenkinson family, Montebello family, Duchess, French, straight coiffure, turban, ferroniere, modesty piece, scoop neckline, bodice, vee neckline, full skirt, floral bodice ornament