From Wikimedia; a limited number of spots in background were removed with Photoshop by gogm.
Duchess Emily wears robes over a British casual dress with a fichu in this Reynolds portraits from the 1770s.
Keywords: Reynolds, Emily FitzGerald, Lennox family, Stuart family, FitzGerald family, Countess, high straight coiffure, turban, scoop neckline, fichu, waist band, robes