I cannot find anything about her other than this portrait.
From the Christie’s Web site. Also posted to the Reign of Louis XV - 1715 to 1774 Album.
The short hair dates this to before 1760 and the cuffs set this to the 40s or earlier. Wired caps came in around the 40s. Her neckline area is covered by a fichu, a piece of dress that would become prominent in the 1780s.
Keywords: Wills, Ann Burney, straight coiffure, bows, lace wired cap, earrings, necklace, fichu, trapezoidal neckline, bodice, U-neckline, three quarter length close sleeves, turned back cuffs, turned back cuffs, lace-trimmed engageantes, lace-trimmed stomacher