UsMagazine.com said the stylish 49-year-old mother of two also wore a handmade diamond embellished ring by Kimberly McDonald paired with Jimmy Choo shoes.
Wu previously created the one-shouldered white frock Mrs. Obama wore in 2009 to the first inauguration celebration for her husband, President Barack Obama.
The president, who looked dapper in a black tuxedo and white bowtie, hit the dance floor at the Commander-in-Chief ball for military families Monday night as Oscar-winning entertainer Jennifer Hudson sang her rendition of Al Green's classic "Let's Stay Together," UsMagazine.com said.
The first couple were also expected to drop by a larger celebration open to the public later in the evening.
Swim Week Miami Beach 2014 [PHOTOS]