Her article in thepeerage is here.
From artuk.org; shadows slightly filled in. Also posted to the Reign of Louis XVI Album here.
Henrietta looks almost like she threw her ensemble together. The major parts are the coat, with its unusual sleeves, and the neckerchief.
Keywords: Hoare, Henrietta Boyle, Henrietta O’Neill, Boyle family, O’Neill family, British, curly coiffure, jeweled feathered headdress, neckerchief, trapezoidal neckline, chemise, lace modesty piece, long under-sleeves, cuffs, coat, draped jeweled bodice ornament, full elbow length upper over-sleeves, tight long lower over-sleeves, girdle, close skirt, wrap