From eBay. This is one of several prints of beauties in Queen Victoria's court released in 1849. The original was prepared a decade or so earlier based on her dress.
Lady Sarah's dress has a wide belt and natural waistline while her coiffure with flourishes of curls is later 1830s or 1840s.
Keywords: Beresford family, Chetwynd-Talbot family, Countess, British, straight coiffure, off shoulder vee neckline, modesty piece, rosettes, belt, natural waistline, full skirt, necklace, wrap, lace