Diane Darcy was a female race car driver who was one of the contestants of the Trans-France Race. She was an attractive woman with strawberry-blonde hair and hazel eyes. For the race, Diane wore a white jumpsuit with three dark blue stripes on each shoulder, and decals bearing such names as Dover Fan Belts, Sure-Power Spark Plugs, and Nationale. Her car was a powder blue 1976 Lancia Scorpion with yellow and white stripes and a number 7, called Giselle, who also had a mind of her own. Initially, Diane seemed to hate Jim, and did not believe that Herbie was in love with her race car.
Diane was a woman who fostered dreams of success as a race car driver, and serving as a positive role model for young women who wish to do the same. But when Herbie, the "Love Bug", came to Paris, France, with the crew of driver Jim Douglas and mechanic Wheely Applegate, Diane's dreams seemed to be in jeopardy, for Herbie had begun to fall in love with Diane's Lancia (Herbie Goes to Monte Carlo).
Diane and Jim split after Monte Carlo. She later met Jim Douglas again later, when she went to his bachelor party. She caused conflict when Jim's to-be-wife, thought that Diane and Jim were having an affair. Later that day, she won a race in Herbie, with Jim and his wife getting back together. (HerbieTV: My House Is Your House)