Vanessa Doofenshmirtz

Vanessa Doofenshmirtz is a recurring character in Phineas and Ferb, and the daughter of Heinz and Charlene Doofenshmirtz. She was born on the 15th of June, coincidentally the same day as Linda and Lawrence's wedding anniversary. ("Dude, We're Getting the Band Back Together") She can not be considered an antagonist but she sometimes helps her father with his schemes

Trivia :

 * Vanessa was Kyle's old girlfriend and now they're just allies and friends.