Her Wikipedia article is here. She married three times, the third time to Charles Seymour, 6th Duke of Somerset after marrying Henry Cavendish and then Thomas Thynne. She was the daughter of Lady Elizabeth Wriothesley. She had four children, all by Charles Seymour.
From ellesbelles_1909's photostream on flickr; spots in background removed with Photoshop by gogm.
Eleven year-old Elizabeth wears a curly coiffure and a dress with vee neckline and puffed sleeves with lace engageantes just like the grownups for her 1678 Gascar portrait.
Keywords: 1678, Gascar, Countess Elizabeth of Ogle, Duchess Elizabeth of Somerset, Percy family, Cavendish family, Thynne family, Seymour family, Duchess, British, curly coiffure, off shoulder vee neckline, chemise, modesty piece, elbow length puffed sleeves, engageantes, lace, split bodice, quarter length puffed sleeves, waist band, vee waistline, close skirt, necklace, earrings