Gertrude "Gigi" Hollingsworth is a classmate of Alex and Harper, as well as a rival to Alex. Their rivalry is dated back to kindergarten when Gigi spilled juice on Alex's mat and then told everyone Alex had an accident. She also targets Harper in the episode Alex's Choice and invites Harper to her annual tea party to crown her the biggest loser.
Gigi does not torment Alex and Harper alone; she has a duo of girls that bow down to Gigi's many whims.
Gigi's quest to make Alex look bad almost outs the Russos as wizards when Gigi gets into Alex's private journal and lives in Alex's medieval fantasies. Other than Harper, she can be considered as the character closest to finding out the Russo secret.