Margaret Georgiana, Countess Spencer, née Poyntz by Henry Pierce Bone after Sir Joshua Reynolds (auctioned by Christie's)
From Wikimedia.
Georgiana Poyntz may be dressed in oriental style for this Reynolds portrait. Christie's lot notes for this follow, "HENRY PIERCE BONE (BRITISH, 1779-1855), AFTER SIR JOSHUA REYNOLDS, P.R.A. Margaret Georgiana, Countess Spencer, née Poyntz (1737-1814), seated on a red draped chair, one hand raised to her cheek, in a gold-trimmed white dress and gauze head scarf over her powdered hair dressed in ringlets, stormy sky background signed, dated and fully inscribed on the counter-enamel 'Georgiana daughter of the Rt. Honble. Stephen Poyntz of Midgham, Co: Berks: wife of John 1st Earl Spencer. nat:1738. ob:1814 London. Jany. 1833. Painted by Henry Pierce Bone, Enamel Painter to Her Majesty, & their Royal Highnesses the Duchess of Kent & Princess Victoria after the original by Sr. Joshua Reynolds in the possession of the Honble. Wm. Ponsonby'"
Keywords: Bone - Henry, Reynolds, Georgiana Poyntz, Poyntz family, Spencer family, Countess, British, long straight coiffure, turban, veil, trapezoidal beckline, chemise, criss-cross bodice, vee décolletage, long tight sleeves, cuffs, waist band, close skirt, theatrical dress