Candace is part of a blended family, a decision made after an experience Swampy Marsh had in his childhood. In the series, she has two younger brothers, Phineas Flynn and Ferb Fletcher, with Phineas being a biological brother and Ferb a step-brother. Her best friend is Stacy Hirano. Candace speaks in a valley girl accent, especially when conversing with Stacy. Her birthday is on July 11.
Unbeknownst to her and the other family members, their pet platypus, Perry, is an espionage agent who fights Dr. Doofenshmirtz, an evil genius. She is unaware that his battle with Dr. Doofenshmirtz is the cause of many Phineas and Ferb's inventions' disappearances.
In "Phineas and Ferb's Quantum Boogaloo", it is shown that she will have three children in the future: Xavier, Fred and Amanda. In "Great Balls of Water" it is revealed that she plays 20 different instruments that start with "B".
Povenmire described the character: "Candace does get frustrated. She thinks it's not fair -- that if she were doing the things they're doing, she'd get in trouble. It's not, 'I'm going to get those guys and ruin their lives.' She does bust them later in the season, but there are a couple of twists to it."
Her personality was based on Jennifer Grey's character in Ferris Bueller's Day Off and the actress had previously portrayed Doofenshmirtz's professor in "Oil on Candace."
All characters in Phineas and Ferb were drawn in a design borrowed from Tex Avery's style, with geometric shapes being included in their structure; Candace in particular is that of a circle.
Candace's catchphrases follow, "Mom! Phineas and Ferb are..." and "You are so busted!"
One of the show's running gags revolves around Candace's character. An antagonist, Candace has been noted to hold an obsession over tattletaling the creations of Phineas and Ferb, referred to in the series as "busting." While she repeatedly fails in proving the extravagances to her mother, Candace has remained persistent in the majority of episodes. Whenever Candace carries her mother to the project site, Phineas and Ferb's work unintentionally disappears or is hidden before their mother sees it; the boys then appear to be involved in simple activities deemed normal. Usually, Candace stutters and sometimes, her mother forcibly takes her away, disregarding Candace's actions as crazy and childish.
In some episodes, Candace brings evidence to her mother, but it is misplaced or lost.
While the main reason Candace is motivated to succeed in busting her brothers is described in "Rollercoaster" as proving superiority over them, one reason to bust them is shown in Phineas and Ferb the Movie: Across the 2nd Dimension, when she tells "the force that stops her from busting her brothers" to stop so she can protect them from themselves. The so-called "force" is Candace's developed superstition for the miraculous disappearance of Phineas and Ferb's projects as she attempts to show them to their mother. A third reason is implied in the song "Busted" sung by Candace and Vanessa, which is to prove she was always right--and not crazy, as her mother seems to believe.
In "Phineas and Ferb's Quantum Boogaloo," it is revealed that if she ever did bust her brothers, it would result in the complete ban of creativity, thus leading to Dr. Heinz Doofenshmirtz, as whom she is, in her attempts to bust them, almost as evil, achieving his goal of taking over the Tri-State Area (Plot-B), unless she manages to bust them when it would not matter.
Another running gag in the series is that Candace, while typically shown as a reasonably attractive girl, is not at all photogenic; quite the contrary is true. Pictures and videos of her are rarely flattering, showing her in an awkward pose or embarrassing expression--leading to her fear that Jeremy will see them. Unfortunately for her, it seems that the more unflattering the picture, the more public exposure it gets; for instance, a particularly mortifying picture of her was once put on the side of a blimp.
Candace has a leitmotif: a frenzied rendition of a child's taunting song.
It was mentioned in "Let's Take a Quiz" that she has an allergy to both dairy products and beetroot. She is also allergic to wild parsnips (see the Season One episode "Jerk de Soleil" and Phineas and Ferb the Movie: Across the 2nd Dimension). She is friends with Vanessa Doofenshmirtz, the daughter of Perry's nemesis, Dr. Heinz Doofenshmirtz, and has been to his lair on a number of occasions but is still unaware of where Perry goes everyday, whereas Vanessa, who knows Perry personally, is unaware of the fact that Candace is part of Perry's host family.
When not trying to bust Phineas and Ferb, Candace is usually doing something related to Jeremy Johnson, her boyfriend. She often over complicates things in their relationships and worries that Jeremy doesn't like her when in truth he is always shown to care deeply for her: Candace's insecurity blinds her to the fact that she has already won him over.
Candace tends to get annoyed with Perry when he gets to her bed while she's sleeping. Although she gets annoyed with Perry, she does generally care for him, as seen in such episodes as "Mom's Birthday", "Traffic Cam Caper" and "Sidetracked". Candace blamed herself for Perry's disappearance in "Oh, There You Are, Perry" when he was actually reassigned to a more dangerous villain. Candace saw Perry as a secret agent two times while she was dreaming or hallucinating, as it was seen in episodes "The Ballad of Badbeard" and "Wizard of Odd". ("Phineas and Ferb Gets Busted" doesn't count, considering Perry was the one dreaming about Candace dreaming.)
There is a recurring (but unexplained) zebra that pops up whenever Candace is dreaming or hallucinating that calls her "Kevin". At one point she asked Phineas and Ferb about it, and they claimed to have no knowledge of it.
Despite being somewhat selfish and often looking down on her brothers as mere annoyances, Candace, loves them at her heart and has shown them affection in episodes like "Dude, We're Getting the Band Back Together", "Phineas' Birthday Clip-O-Rama", "Lights, Candace, Action", and "Phineas and Ferb: Summer Belongs To You", where she sings about how proud she is of the boys. Candace also allows herself to enjoy her brother's inventions every so often. Although Candace frequently overlooks the fact that Phineas and Ferb openly care about her, she is shown to care more about their well-being than busting them. In "Traffic Cam Caper," when Phineas is in peril, Candace goes out of her way to save Phineas, allowing a disc containing footage of their projects to be stolen by Perry the Platypus. Also, when Phineas delivers a heartfelt speech at his birthday party thanking his friends, Candace is so touched that she destroys yet another disc that was intended to bust him ("Clipshow"). She is even unable to defend herself against evil robots that merely look like Phineas. In return, Phineas has been shown to go to great lengths to rescue Candace when she is endangered.
Common Sense Media rated Candace as the 10th worst TV role model, claiming that "her primary motivations are pleasing her boyfriend and getting her brothers in trouble" and she was "a screechy, whiny stereotype of a girl", which could reinforce gender stereotypes.