Margo Sherman is Jay's younger sister and the only biological daughter of Franklin and Eleanor Sherman. She is a 17 years old and a high school senior at Miss Hathaway's School for Untouched Girls. Margo is also an activist who often protests her mother's WASP lifestyle.
Margo is a relatively thin brunette. Her normal outfit is comprised of a green hoodie with a lilac headband and light blue jeans. Surprisingly, she does not outright resemble either of her parents.
Margo cares deeply for Jay. Even going so far as to proclaim that of all things in the world she loves her brother and her horse the most. She makes sure that many of his girlfriends are not just dating him to get a good review on their movies. Jay also escorts Margo to the debutante ball in which thier mother forces her to go.
In Season 2, Margo briefly dates grunge rock singer Johnny Wrath after he moves next door to her. She even considered losing her virginity to him, but soon discovers he was cheating on her and quickly breaks off the relationship.
- Margo went through one of the more drastic design changes of season two. She became more stylized with rounder features and also lacks the pink lipstick from her initial design.
- Even though she is voiced by Nancy Cartwright, who is famous for playing a multitude of different voices, Margo's voice is more akin to that of Nancy's natural speaking voice.