Her article in thepeerage is here. Her Wikipedia article is here.
From Wikimedia.
Lady Dorothy Sydney’s lower sleeves are very full and they, or their lining, are of a contrasting color. The next image is a close up.
Keywords: 1650, van Dyck, Dorothy Sidney, Dorothy Spencer, Countess of Sunderland, Saccharissa, Sydney family, Spencer family, Countess, British, proto-hurluberlu coiffure, floral headdress, earrings, necklace, chemise, modesty piece, off shoulder scoop décolletage, bodice, brooch, clasps, three quarter length puffed sleeves, contrasting cuffs, wrap