But the woman who put unstuffy retailers like J. Crew on the fashion map also showed a weakness for high-end fashion "a la francaise," taking her two daughters on a private shopping trip to the exclusive children's couture house Bonpoint.
Mrs. Obama's visit to the City of Light was widely billed as a rematch of the "duel of charm" that pitted her in a glamour contest against France's first lady, the former supermodel-turned-singer Carla Bruni-Sarkozy.
The heels were a departure for Bruni-Sarkozy, a leggy Italian-born heiress who leaped to fame in the early 1990s as a top model. Since she married France's diminutive leader Nicolas Sarkozy last year, the 5'9" (175 centimeter) -tall first lady has largely stuck to flats for her public appearances.
Bruni-Sarkozy's outfit, which also included a swingy black cashmere coat, was signed Christian Dior - her favorite label. Also true to form, Mrs. Obama's dress was by Narciso Rodriguez, one of the stable of American designers she champions.
Britain's Daily Telegraph said photos of the two striding side-by-side on the red carpet at Saturday's commemorations were "surreally interchangeable with shots from a catwalk show. ... They could almost have been modeling some designers' collection named 'First Lady Spring 2009."'
French fashion weekly Elle said the two looked like "twin sisters" and hailed their "sophisticated, feminine" 1950s-era looks as "a success: We want more!"
A similar thing happened at their last meeting, at a G-8 summit in the French border city of Strasbourg in April, when both showed up in stylish but proper coats embellished with flowing bows at the neckline and coordinated with matching dresses.
Then, the European fashion press generally concurred that Mrs. Obama's Thakoon ensemble, in black silk with fuchsia flowers, stole the show from Bruni-Sarkozy's Dior outfit in putty gray.
But it appeared that Bruni-Sarkozy's sophisticated Parisian style might be winning Mrs. Obama over.
On Sunday, the American first lady and daughters Malia, 10, and Sasha, 7, went shopping at Bonpoint, a children's clothing store favored by wealthy Parisians and international jet-setters like Sofia Coppola.
Bonpoint's store in the tony Saint Germain des Pres neighborhood was closed for inventory on Monday and store officials were not available to discuss what, if anything, they bought. The brand, known for its airy stores carrying cashmere baby sweaters and smocked pastel frocks, was a far cry from CrewCuts, J. Crew's children's line, which the Obama girls wore to the inauguration.
Mrs. Obama and the girls met up with the president in Paris, on the last leg of his six-day tour of four Middle Eastern and European countries. Obama left Paris for Washington, D.C., on Sunday morning, leaving his wife and children to enjoy the French capital on their own.
Apart from the D-Day commemorations, Mrs. Obama's Paris visit was a private one, closed to the press. Photographers and camera crews caught images of her and the girls visiting the city's must-see monuments, including the Eiffel Tower, the Louvre, the Pompidou Center modern art museum and Notre Dame cathedral.
For those visits, Mrs. Obama stuck to her signature looks, wearing cardigans and flats for her trip to Bonpoint and a teal jacket and printed scarf for the Eiffel Tower.
Mrs. Obama and the girls also attended a private luncheon hosted by the Sarkozys. The event, at the gilded Elysee presidential palace, looked like an advance fete for Sasha's 8th birthday this Wednesday.
It wasn't immediately clear what Mrs. Obama or Bruni-Sarkozy wore to the lunch, so fashion-watchers will have to hold on for Round 3 of the first ladies' fashion face-off.