She was Princess of Wales Augusta's daughter and sister of George III. Her Wikipedia article is here.
From Wikimedia; linear flaws removed with Photoshop by gogm.
Princess Louisa wears a gorgeous dress fairly oozing lace on her modesty piece, revers, stomacher where it is mixed with bows, and engageantes. She also wears a floating ruff of lace around her neck.
Keywords: 1767, Princess Louisa of Great Britain, Welf family, Princess, British, straight coiffure, floating ruff, lace, square neckline, modesty piece, revers, stomacher, bows, three quarter length close sleeves, engageantes, earrings, gloves, fan