From Wikimedia; spots throughout image removed with Photoshop by gogm.
Lady Jane's coiffure is very feminine, but her equestrian dress with double-breast button rows and vest shows masculine influences dominate. I am unsure of how her hat is to fit on her towering coiffure or how the coiffure, with or without hat, would function when riding at a gallop.
Keywords: 1775, Gardner, Jane Maxwell, Maxwell Family, Gordon family, Duchess, British, high straight coiffure, feathered hat, chemise, high enclosing neckline, long tight sleeves, ruffles, jabot, lace, jacket, vee neckline, lapels, buttons, cuffs, vest, natural low neckline, full skirt, pin, gloves, equestrian dress