She's the only female race car driver in the Trans-France Race and first meets Jim Douglas by accident when they bump into each other.
She owns a 1976 Lancia Scorpion which, like Herbie, is alive, however, she didn't know it at the time. When Herbie first sees her car, he falls in love and Diane gets annoyed every time he gets in the way while racing. She starts accusing Jim and Wheely of trying to keep her out of the race because she's a woman driver.
As the film goes on, she learns to like Jim and finally believes her car is alive and encourages Herbie to win the race for his friends and for his loved one.
In the end, she starts dating Jim and names her car "Giselle."
Diane returns in the third episode of the series. She discovers Jim is now dating another woman named Susan MacLane but it is clear they are just good friends. She's last seen racing Herbie when Susan thought it was Jim behind the wheel.