Vanessa tends to be sarcastic and generally acts like a normal teenager. She cares about her reputation, especially when her clothing gets switched with Candace's clothes. Vanessa has always hung out with the "goth" crowd, as seen in her childhood photos and her group of friends ("Hail Doofania!", "Dude, We're Getting the Band Back Together", "Brain Drain").
Her desire to have a car of her own is quite clear. She tries to prove she is responsible enough to own her own car by trying to get a rare element her father needs in the Super Duper Supermall ("Vanessassary Roughness"). This is also evident when Doofensmirtz told her he'd brought her a gift, she exclaimed "A car!" with excitement and was disappointed when she found out it was just a doll that she had wanted when she was a little girl. ("Finding Mary McGuffin")
She is, or at least was, on her school's swimming team. She also took ballet as a young girl. ("Finding Mary McGuffin")
Although she tries to deny it when around her father, she is a little evil, as evidenced in "Phineas and Ferb: Summer Belongs To You!," when Phineas remarked about her renting a scooter and her responding, "Yeah... rented," implying she stole it. She also took the Mary McGuffin doll from a little girl, and has aided in parts of her father's plans. Also, she admits that she's at least a little evil.