Frances Cotton's article in thepeerage is here.
From Google Art Project via Wikimedia.
Lady Frances' dress has tabbed sleeves, hanging sleeves, and the deep vee waistline of what appears to be a wheel farthingale. Her dress could have a partlet supporting the jewel on her neckline or it could be the pendant of a necklace hidden by her elliptical ruff.
Keywords: Peake - Robert the Elder, Francess Cotton, Lady Montagu, Cotton family, Montagu family, Baroness, British, frizzy coiffure, jeweled feathered headdress, lace floating ruff, bodice, lace modesty piece, lace bertha, tabbed sleeves, hanging sleeves, long close sleeves, lace back-flared cuffs, deep vee waistline, wheel farthingale, earrings, pendant, brooch, bracelets