"Candace: I call you snail, HA! Wendy: You, we're quick!." — Wendy To Candace when Wendy was slow[source]
Wendy is a hyperactive, motivated, and enthusiastic teenage girl, and a possible rival to Candace Flynn for Jeremy's affections.
When Jeremy suggests to Candace that she takes the job opening at Mr. Slushy Burger so they can work side-by-side, Wendy suddenly steps in, offering to apply for the job, much to Candace's annoyance. But since there's only one opening, the manager suggests they compete to see who is a better choice for the job. For their first task, the two of them are supposed to dress some hot dogs with ketchup and mustard. But Candace and Wendy end up turning their contest into a food fight with both of them throwing the food dressing at each other, which results in both of them losing the job opening. ("Unfair Science Fair")
At the beginning of "Unfair Science Fair Redux (Another Story)", Wendy is among the people Candace tries to call, asking to hang out; Candace mentions there that they shared a seat on the bus to the planetarium.
Wendy has short black hair that is kept back by a purple headband. She wears a purple dress over a shirt with a lighter shade of purple. Her dress shares similarity to Isabella's.
Candace was her opponent for the job position. But, as mentioned above, they did once sit together on the ride to the planetarium and Candace has her phone number. Both are sort of having a 50-50 relationship with each other as friends.
In "Unfair Science Fair Redux (Another Story)", Candace calls her name and mentions it; it may be other person named Wendy but has believe which may be Wendy who Candace proclaims 'Hi, Wendy can we go to the planetarium'.
Brenda Song, who voices Wendy, and Ashley Tisdale, who voices Candace, both starred together in the Disney Channel series, The Suite Life of Zack and Cody where they both played each other's best friend.
Wendy resembles Brenda Song since they both have dark skin and black hair.
Candace was originally supposed to be blonde like Ashley, which would've furthered the connection.
Brenda Song plays a similar character in Wendy Wu: Homecoming Warrior. In this case, this character is probably based on Wendy, since they resemble each other, are competitive, and have the same first name.
Her name was not mentioned in the episode, but she was named in the end credits.