According to her Wikipedia article, Maria Elisabeth married in 1808. This could be a wedding portrait, but it was auctioned with a portrait of her husband dressed as a Restoration-era soldier. Their auction notes state it was one of the last portraits for Louis Alexandre Berthier who died in 1815. She was the daughter of Maria Anna of Zweibrücken-Birkenfeld. The Berthiers had one son, Napoléon Alexandre, and two daughters, Caroline Josephine and Marie Anne.
From Wikimedia.
Marie Elisabeth's dress is decorated with a bertha ending in a leafy or floral fringe. She wears a ferroniere and a tiara beneath her lace veil.
Keywords: Boze, Maria Elisabeth Wittelsbach, marechale Berthier, Herzogin in Bayern, Duchess in Bavaria, Maria Elizabeth Amalie Franziska Wagram in Bayern, Maria Elizabeth Amalie Franziska Wagram of Bavaria, princesse de Wagram, Princess Wagram, Fürstin von Wagram und Herzogin von Neuchâtel, Princess of Wagram and Duchess of Neuchâtel, Wittelsbach family, Berthier family, Duchess, Princess, French, curly coiffure, tiara, ferroniere, lace veil, necklace, earrings, square neckline, lace-edged bertha, order bows, quarter length full sleeves, waist band, Empire low waistline, close skirt, wrap