Her article in thepeerage is here. Her grandmother's portrait is here.
Lady Jermyn wears a bateau neckline framed by a white modesty piece over a close skirt. The dress appears to have slashed sleeves clasped to the bodice.
Keywords: 1657, Henrietta Jermyn, Jermyn family, Gage family, hurluberlu coiffure, bun, jeweled headdress, trapezoidal neckline, chemise, modesty piece, three quarter length puffed sleeves, bodice, strap over-sleeves, elbow length puffed under-sleeves, slashed sleeves, close skirt, necklace, earrings, clasps