Urban and wife Nicole Kidman performed a duet of the country star's song "Female" in honor of the special day, a performance that was subsequently filmed by their daughters, Sunday and Faith, and posted by the actress to Instagram. RELATED: Michelle Obama: Educate every girlKidman is featured in the background vocals on the studio version of the song, but has never performed it with her husband in public. "Of all songs to have her sing on, it was the right one," Urban told E! last year. The United Nations has celebrated International Day of the Girl since 2012 to promote girls' empowerment and highlight the various challenges girls around the world face in their quest to be treated equally, receive education and reach their full potential.Kidman has been a Goodwill Ambassador of UN Women since 2006.