Diana (Julie Payne) is the main villainess from "Rainy Day Dreams," a second season episode of Garfield and Friends (airdate October 28, 1989).
Diana is a sleazy insurance salesman who cozied up to Jon Arbuckle in an attempt to sell insurance to him. After meeting Jon, Diana arrived with her partner and boasted about how Jon fell for her, stating that he'll buy so much insurance that they can retire. The smitten and gullible Jon lets Diana in and makes attempts to woo her, while Diana focuses on her plan to sell insurance.
Diana had obstacles in the form of Garfield and Odie, who had been spending the rainy day using their imaginations and pretending to have adventures. In one scenario, Garfield and Odie wander around in a cave (the bedroom) when they encounter a dragon (Diana), prompting Garfield to drench Diana with a bucket of water. After Diana dries off and lays down, she is again thrust into the pets' imaginations, as Garfield and Odie pounce on Diana, who they imagine is the Bride of Frankenstein.
It was during this that Jon learned about Diana's ruse, as Garfield and Odie caused her insurance forms to spill out. Following this, a furious and defeated Diana leaves in a huff.