The Popular Girl is an unnamed girl who goes to Nora's school, seen only in the episode iPsycho. She came to Nora's party after the word got out that the iCarly gang was attending. She was friendly to Nora. Nora kisses her and she obviously felt weird about it. She also asked Nora if she would come get mani-pedis with her and her friends. Nora said "Oh, yes. I would love to get a mani and a pedi with girls."
She is portrayed by Daniella Monet, best known for playing Trina Vega, the diva on Victorious. Monet's appearance meant she was absent from the filming of some episodes of the show, so her character was absent for a few episodes.
(text taken from the iCarly wiki)