B's night out

Beyoncé at the 40/40 Club on Feb. 7

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Even new moms have to get their dance on! And Beyoncé did just that Friday night. She joined younger sister Solange and two female friends for a girls' night out at New York City's W.I.P. nightclub. "B" let loose on the dance floor and jammed to the club's mix of disco, '90s and hip-hop music.

"Beyoncé looked amazing and was having a great time with her friends," an onlooker tells PEOPLE. "She was very laid back, smiling and in a great mood."