This could be Lady Elizabeth Frances Villiers. According to her article in thepeerage, she was born in 1786 and she married John Ponsonby in 1803.
From portraitminiature.blogspot.com/2009/10/19th-century-miniatures-1806-1820.
Lady Ponsonby is dressed in the height of Directoire style with sleeves and waist marked by bands and a wrap for protection.
Keywords: 1810, Knight, Elizabeth Frances Villiers, Fanny Ponsonby, Viscountess Ponsonby of Imokilly, Villiers family, Ponsonby family, Viscountess, British, long straight coiffure, off shoulder straight neckline, quarter length tight sleeves, arm bands, waist band, Empire waistline, wrap