Jen is a sensible red-haired girl who is the gang's voice of logic and reason and a big-sister surrogate to Caitlin. She works sales at the Penalty Box, where she has to deal with her boss, the gruff and thick-headed Coach Halder, who often yells "MASTERSON!" at her and sends her to the store's physical penalty box for perceived infractions. She loves shopping with Caitlin, to whom Jen gave her old job at the Big Squeeze upon moving to the Penalty Box. She has an older sister named Courtney, of whom she is envious, and a new baby half-sister named Emma (named after her mother), and she later became Jonesy's stepsister.
- Jen is the only one of 6teen's three main female characters who does not wear eyeshadow
- She reveals her full first name while in the computer survey booth in "Oops, I Dialed It Again". Later, in the series finale "Bye Bye Nikki? (2)", her full name, Jennifer Anne Masterson, is revealed on her prerecorded greeting on her cell phone voice mail as Nikki tries to contact her
- Her voice has a tendency to become squeaky when she becomes excited, angry or emotional in other ways
- Her name in the French-language version of the series is Julie Maréchal
- In 6teen's original pre-development incarnation as The Mall, Jen was a brunette who wore her hair in twin pigtails, and she also wore a yellow bandana in her hair and a yellow hoodie, all of which was changed, along with her general appearance, during series development