Gretchen has shoulder length brunette hair, and she is the only brunette in the plastics. She has brown eyes and wears makeup throughout the film, significantly more than her fellow Plastics. She mentions that she enjoyed wearing hoop earrings as a personal accessory for quite some time, but was forced to give them up by Regina.
She appears very close to Karen Smith and frequently watches out for her. For example, when Karen admits to her that she has kissed her first cousin Seth, she tries to help Karen understand that it's wrong to be romantically involved with someone with whom you share relations. When Regina calls her a slut, Gretchen seems to feel bad for her and takes it upon herself to tell Karen. When Gretchen, Cady, and Karen are sent to the principal's office for the Burn Book, Gretchen does not tell on Karen or Cady. In they gym, she keeps Karen from talking about "girl problems," possibly trying to keep Karen from saying something she would later regret. She seems to accept Karen's apology, and in return, Karen is the only girl to catch Gretchen when she does her trust fall off the table.
Her relationship with Regina is a complicated one. While its clear that Regina has confided a large amount of personal secrets in Gretchen, Gretchen often ends up spilling them without meaning to. After a slip up, she always says "Don't tell Regina I told you that." Regina is overly controlling and Gretchen is clingy, willing to do anything to keep Regina's trust and friendship. For example, she promised Cady she would keep her attraction to Regina's former boyfriend a secret, but gives the information over to her without a second thought. She gave up wearing hoop earrings when Regina told her she must, going so far as to turn down a pair of expensive white gold ones her parents gave her for Hanukkah. She knows that Regina cheats on Aaron Samuels with Shane Oman, and seems to feel remorseful about it, but never tells anyone until she confesses to Cady. She is distressed, when Cady receives a candy cane from Regina and she does not. At the Winter Talent Show for the plastics performance of Jingle Bell Rock performance, she overreacts when Regina tells her to switch places with Cady, claiming she is "always" on Regina's left. When performing, there is visible space between her and the other Plastics, as though Regina's "rejection" had her unsure of her place in the group. When Regina cried over losing Aaron and claimed no one understood her, Gretchen ran after her saying "I understand you, please talk to me!" As Cady says "The meaner Regina was, the harder Gretchen tried to win her back."