1781 Lady Elizabeth Compton by Sir Joshua Reynolds (National Gallery of Art - Washington, DC USA)
From www.wikipaintings.org/en/joshua-reynolds/. I cannot locate a higher-quality version of this image.
British casual style dresses did not change for decades, even if the coiffures did as seen in this 1781 Reynolds portrait of Lady Elizabeth Compton.
Keywords: 1781, Reynolds, Elizabeth Compton, Compton family, Cavendish family, Countess, British, high straight coiffure, ribbon headdress, coat, long full sleeves, criss-cross bodice, scoop décolletage, shallow vee waistline, close skirt, shoes, necklace