Agnes is first introduced as a wild young model who is employed by Eleanor Waldorf's atelier. She befriends Jenny and brings out her wild side. It is actually Agnes who encourages Jenny to leave Eleanor's employment, who has been taking some of Jenny's designs, and start her own fashion line. Jenny leaves her family to start her own fashion line but Agnes's lazy ways keep Jenny from succeeding, despite her talents. When Jenny decides to leave Agnes and be the sole owner of her line, Agnes burns all of Jenny's clothes as revenge.
Agnes later resurfaces in Season 3 when Jenny is again working for Eleanor in one of her fashion shows. Although she and Jenny apparently make up for what happened the year before, Agnes ends up drugging Jenny and leaves her at a gentleman's club hoping that she will be raped by one of the men there, however she doesn't expect Nate to save her.
Agnes returns in Season 6 for the final episode of the show, saying "That little bitch!" as Gossip girl is revealed.