She was initially foreshadowed as a possible owner of the mineral rights under the Smith property in "Mine Struggle". It is also noted that she would star in an upcoming episode about slot cars.
When Francine becomes suspicious that Stan may be cheating on her with Diane, she slips into CIA Headquarters but is caught by Diane. She brushes it off, convinced she will find them having sex in Stan's office, but when she kicks in the door, she finds him playing with slot cars. With Stan's regressed behavior and new habits, she finds that Diane doesn't consider him sexy at all.
Diane is voiced by Paget Brewster.