She is the duchesse de Polignac’s granddaughter and Aglaé de Gramont’s daughter who, according to this genealogical sketch, married Russian General Alexander Davydov in 1805 and, later in 1831, married Général de l’Empire François Horace Bastien Sebastiani de la Porta.
Accordong to The Art History Archive, Élisabeth Louise Vigée-Lebrun was in Russia between 1795 and 1801. Sotheby’s NOTA DEL CATÁLOGO includes this, "Vigée Le Brun’s portrait of the blue-eyed and still strikingly beautiful Aglaé Angélique Davydova, despite her thirty-seven years, depicts her subject in the open air against a cloudy sky. She is attired in a short-sleeved velvet gown with a deep neckline over a muslin chemise with gold trim, and around her long neck hangs a gold chain to which is attached a gold pendant. Her dark hair is styled in ringlets, or "anglaises" falling onto her brow, and those strands that are piled high on her head are held in place with a gold and coral diadem. Over this hairdo is draped a muslin veil she clasps to her bosom with the long, tapering fingers of the hands crossed over her breast, and the end of this length of sheer fabric floats in the wind behind her. The portrait was executed by the artist around 1824, the year of Louis XVIII’s death and the accession of his brother, Charles Philippe, Comte d’Artois, to the throne of France as Charles X."
Upgrade image posted 26 August 2017 from Wikimedia. Also posted, perhaps arbitrarily, to the Russian Style in the French Revolutionary Era Album here.