According to her Wikipedia article, that has this image, Princess Mária Antonia's son married Queen Maria II of Portugal and became King and King-Regent of Portugal as a result, her son August married Princess Clementine of Orléans, and her daughter Victoria (Victoire) married the Duke de Nemours Louis d'Orléans.
From Wikimedia.
This portrait could commemorate Mária Antónia's engagement or 1815 marriage to Prince Ferdinand. She wears a coiffure and dress that appear to be strongly influenced by Hungarian folk dress.
Keywords: Mária Antónia Koháry, Princess, Koháry family, Wettin family, Princess, Hungarian, braided coiffure, head band, chemise, high neckline, virago sleeves, arm bands, bodice, deep vee décolletage, strap sleeves, belt, Empire waistline, close skirt, frogging, shallow necklace, clasps, wrap