Ke$ha was in for a surprise Saturday when she went to Cipriani 42nd Street to give a surprise performance at what she thought was a Sweet 16 party. The lavish bash was beyond ostentatious, with ballet dancers suspended from the ceiling blowing bubbles and handing out custom-made candy to guests as they arrived. “The gift bags were Juicy and had custom spray-painted sneakers in them,” said one witness. As a giant cake was wheeled out, it was announced that Ke$ha, who allegedly pocketed $50,000 for the gig, would sing two songs. “Everyone flips. Then Ke$ha wishes the girl a happy Sweet 16, and people clap, but with puzzled looks on their faces,” said our witness. “It’s not her Sweet 16. It’s her bat mitzvah.” Kei$ha was evidently misled because many artists will perform for 16-year-olds but not 13-year-olds. Ke$ha’s management company had no comment.