was solid gold in a sparkling dress while celebrating her female artist of the year award at a star-studded Billboard Music Awards
bash at LAVO Las Vegas. Making her entrance near midnight, RiRi held court as industry pals and other winners congratulated her on the night, where she opened the show with a duet of her hit "S&M" with Britney Spears
. Also at the bash: Mentor Jay-Z
and Billboard Millennium Award honoree Beyoncé
's Matthew Morrison
, and Joe Jonas
– who stopped by the DJ booth to get on the mic and say hello to the crowd.