Catherine is an anthropomorphic monkey with a brown complexion. She has long dark auburn hair and bangs, with her long hair tied into a ponytail. She usually wears a blue denim vest, a cream-colored (originally white) turtleneck, and blue pants, usually with red leg warmers.
Catherine is almost the exact opposite of Francine: she likes wearing dresses, is a very responsible person (unlike her sister), and she really loves to shop. She enjoys reading teen magazines and frequently uses the telephone. Like most sisters, Francine and Catherine go through various fights, like how to decorate their room in the episode "Francine Redecorates" and who gets the last soda; however, despite their arguments, they genuinely love each other. She briefly wore lipstick in one scene of "My Dad, the Garbage Man", nail polish in one scene of "Stolen Bike", and got a pedicure in "Muffy Gets Mature", but she usually prefers to keep her appearance natural. In "Is That Kosher?" her sleepwear is a blue nightgown.
- According to "Vomitrocious", it is implied that Catherine is a 10th grader, as she mentioned a classmate named Lucas Hanson who vomited during math period in 5th grade, which occurred five years in the past. She also celebrates her 16th birthday in Season 18, which coincides with this implication as well as most sophomores in high school would be 15 to 16 years old during the duration of the year.
- In "Citizen Frensky", her name is spelled with a "K." It is unknown if this is the correct spelling or not, because it has also been used with a "C" in other episodes.
- She, like her family, is Jewish.
- In "Play it Again, D.W." and "D.W.'s Name Game", she is the babysitter for Arthur and D.W.
- "The Master Builders" reveals that she goes to a CTE (Career and Technical Education) school, and she wants to be a designer. Her school has a 3D printer.