In her telling, Mr. Mugrabi casually proposed to her at the apartment in 2004, after his mother was nudging him on the phone about wanting to throw an engagement party. “He didn’t have a ring, but I said, ‘You don’t need a ring to propose,’” Ms. Mugrabi said. So he popped the question (she said yes) and called his mother right back. “His mother said, ‘I’m throwing you a party tomorrow.’”

The five-carat diamond ring would come later.

The couple wed in 2005 at an extravagant ceremony at the Pierre hotel that featured orchids dripping from the ceilings and a performance by Ishtar, the Arab-Israeli chanteuse. Ms. Mugrabi wore a custom white-lace gown by Victorio y Lucchino, which required her to visit its atelier in Seville, Spain, for fittings.

“It was way over even what I wanted,” she said. “I knew about 30 people at my wedding. It had about 500 or 600.”

Guests included a who’s who of art-world machers, including Peter Brant, the paper magnate, and his wife, Stephanie Seymour; Aby Rosen, the real estate developer; Larry Gagosian, the high-powered gallery owner; and Steven A. Cohen, the financier who last year bought a prized Roy Lichtenstein painting from Agnes Gund for $165 million.

The newly wed Ms. Mugrabi quickly learned her role in the family empire.

“I just copied his mother, and she told me what to do,” she said. “She’s like, ‘Well, you just do the home part with the entertaining. The way we run our business is mostly through the home, because we don’t have a gallery.’”

For more than a decade, the couple enjoyed the perks of a billionaire lifestyle.

“Every summer we went to Sardinia, to Italy, to Portofino,” Ms. Mugrabi said. “We went on lots of different yachts. Aspen. Miami. We went to St. Barts three times minimum, a year.”