Her article in thepeerage is here. Her daughter Jean's portrait is here.
From bbc.co.
Lady Hay and Mary Beale show how Lely-style portraiture became standard.
Keywords: 1675, Beale - Mary, Lady Mary Hay, Maitland family, Hay family, Marquise, British, long curly coiffure, scoop neckline, chemise, modesty piece, puffed under-sleeves, quarter length sleeves, clasps