Sally has flipped blonde hair with a cluster of curls like Schroeder and Patty. In the early 1960s and in her early television appearances, she is shown to have a bow in her curls. However, this was dropped by 1969. She wears a polka dot dress. In the TV specials, TV series and movies, the dress is colored light blue, although it is usually colored pink in The Peanuts Movie, Peanuts (TV series), and the Sunday strips. In the winter, and most of the time in the later years of the strip, she switched to a (no sleeves or long sleeves) shirt and pants. Sally also wears a long sleeves sweater that usually covers her dress. It is also revealed in the November 13, 1976 comic strip that Sally wears a retainer, meaning she possibly has dental trouble.
Sally is the complex little sister of Charlie Brown. On one hand, she is good-hearted, cute, funny, friendly, sweet, and innocent. However, on the other, she can be lazy, naive, slow, dumb, obsessive, greedy, insecure, and sometimes even self-centered and manipulative.
Sally has a "take it easy" approach to life, preferring to slide by while doing as little work as possible. Her favorite pastime is sitting in her beanbag chair watching TV. One summer, Sally actually went to "beanbag camp," which consisted of nothing but lazing around in beanbags, eating snack foods and watching TV; as a result, she became fat and needed to exercise to lose weight. Sally has a good heart and a strong moral sense; like her older brother she is extremely sensitive to the unfairness of life. Charlie Brown usually goes to Lucy in her psychiatric booth when he is feeling depressed, but Sally prefers to confide her troubles to the school building, which is very protective of her and will drop a brick on anyone who does not treat her nicely.
Sally has a lot of trouble in school. For one thing, she has a problem with malapropisms, both in speech and writing. For example, she says "violins broke out" rather than "violence broke out," or "controversial French" instead of "conversational French". One of the strip's running jokes is the unintentionally humorous school reports she gives at the front of the class, which are frequently inspired by malapropisms and end with her feeling humiliated as all of her classmates laugh at her. Some of the more memorable reports she has given over the years include "Santa and His Rain Gear," "Footbidextrousers" people, and "The Bronchitis" (a dinosaur which supposedly became extinct from coughing too much), and her report on the oceans of the world, in which she reported that there are no oceans in individual landlocked states in the U.S. She often struggles with homework despite Charlie Brown's patient efforts to help her, and she has a particular dislike for math, which she largely finds both intimidating and incomprehensible. However, she has expressed interest in becoming a nurse once she becomes an adult, although this is due to her interest in wearing white shoes, as opposed to the job itself.
Sally also can be very naive. In one strip, she thinks her family is famous, because their name appears in the telephone book. Another time, she is watching TV and wonders why Monday Night Football is not on. When Charlie Brown tells her the day is Wednesday, she says "That's no excuse".
Sally has wanted Charlie Brown's bedroom for years. Every time he either leaves home for a while (such as going to summer camp) or talks about leaving, the first thing she always wants to know is if she can have his room while he is gone. A few times, she has actually begun to move her possessions into her brother's room when she thinks he is never coming home, such as when Charlie Brown fails to come home after falling ill during a baseball game in the strip from July 10, 1979, when he gets lost in the woods in a series of strips from November 1980, and when Snoopy accidentally turns him invisible in the TV special It's Magic, Charlie Brown.
Unlike most of the Peanuts gang, Sally does not seem to have much interest in playing sports. On the rare occasions when she does play, it is usually because Linus invites her. She is one of the few children in the neighborhood who has never played on Charlie Brown's baseball team, and her attempts to play catch with a football usually lead to comic results. She joins a "snow league" in a series of strips from November and December 1973 in which the local adults turn snowman building into an organized sport, but her team is not very good. They lose one match when the referee penalizes them for "improper mittens," and lose another because their snowman is offside.
Being Charlie Brown's sister, she refers to him as "big brother", having called him by his full name only on very rare occasions.