Her terse Wkipedia article is here. Web Gallery of Art has this writeup, "Maréchal Lannes was one of Napoleon's favorite officers, famous for his extraordinary heroism on the battlefield. In 1800 he married Louise-Antoinette-Scholastique Guéhéneuc (1782-1856). It was a happy marriage, Louise-Scholastique was a loving and devoted wife to Lannes. After her husband's death on May 31st 1809, the Maréchale Lannes still played an important role at the imperial court when, after Napoleon's remarriage to Marie-Louise, she was chosen, for her irreproachable morality and virtue, to become Dame d'honneurs (lady-in-waiting) to the new Empress. From about 1814, the year this painting was commissioned, the Duchess of Montebello began to withdraw from public and lead a retired life, devoted to her five children."
From Web Gallery of Art.