Rosalie: Blondes Like it Hot (1984)

Rosalie goes to the big city (Zürich) to work as an assistant to Dr. Palmer. Advised by her colleague she changes her outlook from a sweet, nice girl into a sexy woman, and immediately gets an invitation to spend the weekend with the doctor. When her fiancé comes to visit her, but does not find her home, he and the doctor's wife have a nice time together, then make a plan to get their partners back on the yearly masked ball.