Such scrutiny was practically a national obsession during Mrs. Obama’s White House years, as she notes in her memoir, writing: “It seemed that my clothes mattered more to people than anything I had to say,” and “Optics governed more or less everything in the political world, and I factored this into every outfit.”

That scrutiny has continued through her rare public forays since: at the unveiling of her official portrait at the National Gallery, in which she wore a much discussed geometric -print Milly gown; at the 2017 ESPY Awards, when she presented the Arthur Ashe Courage Award in an asymmetric black Cushnie dress. And it’s only going to get more pronounced as people parse her future intentions through her clothes.

There’s an appetite for the nuanced way Mrs. Obama used fashion both as a tool and a celebration (as opposed to, say, a defensive measure). All of which makes her every fashion choice even more freighted, and none of which has escaped the woman who, starting during Mrs. Obama’s second year in the White House, has helped her put it all together: Meredith Koop. (Ms. Koop styled the Elle shoot, so the clothes reflect Mrs. Obama’s idea of herself, not the magazine’s.)

“I met Meredith when she was a young sales associate about a decade ago, and ever since, I’ve been blessed to have her by my side,” Mrs. Obama wrote in an email. “Together, we’ve prepared for every sort of event — from afternoons in T-shirts and gloves in a garden with middle schoolers to evenings in formal ball gowns with heads of state. Over the years, I’ve come to depend on Meredith for far more than wardrobe. She’s ridden with us through eight hectic years. She’s been a friend and mentor to our daughters. And she’s given us all a sense of comfort and home, no matter where in the world we might be.”