Elizabeth Gillies (Gigi), having a past in musical theatre, performs each of the show's original songs live on set.
The producers were looking for a girl who could sing live, do comedy, drama, and improv. Jim Serpico's teenage sons suggested Elizabeth Gillies as they were fans of the Nickelodeon musical series Victorious. Jim didn't think a Nickelodeon actress could fit into an FX series but Denis heard her sing immediately put the preconceived notions of Nickelodeon behind them.
Gigi mentions Ariana Grande and her fame in several episodes. In real life, Elizabeth Gillies, who portrays Gigi, is good friends with Grande.