Her genealogical information is here. She was the granddaughter of Countess Dorothy Cecil.
From the-athenaeum.org; filled in shadows.
Lady Dorothy’s dress is like many others of the day, but with a sheer covering over a necklace and probable décolletage.
Keywords: Hanneman, Dorothy Allington, Dorothy Leventhorpe, Allington family, Leventhorpe family, British, proto-hurluberlu coiffure, braided chignon, sheer capelet, bows, necklace, modesty piece, square neckline, bodice, U-neckline, puffed upper sleeves