Her article in thepeerage is here.
From Google Art Project via Wikimedia; shadows filled in and exposure increased.
Countess Elizabeth's dress has a plunging neckline concealed by reticella lace and gold jewelry. The farthingale is gone, but hanging sleeves remain. She holds a fan in one hand and appears to be holding a bird in the other.
Keywords: 1619, van Somer, Countess of Kellie, Pierrepoint family, Erskine family, Countess, British, frizzy coiffure, tiara, jeweled feathered headdress, partlet, high enclosing neckline, lace neck ruff, bodice, hanging sleeves, long close sleeves, lace back-flared cuffs, shallow vee waistline, full skirt, maxi-length skirt, shoes, shoe ornaments, pendant, brooch, draped jeweled bodice ornament, bracelets, fan