She was played by Dina Meyer.
Sally Larkin was married to real estate mogul Aaron Larkin, but before the two were wed, Sally signed a prenuptial agreement, a moment she regrets now that the couple are in the middle of a bitter divorce. When she suddenly disappears, Monk is on the case, but after he visits a hypnotherapist, he regresses into childhood and lacks his trademark detective skills. When Aaron turns up dead in a nearby cabin and a disheveled Sally is found, Monk (in his childlike state) states that the story she tells isn't true. When Sally and Monk encounter each other again, the latter (now back to normal) reveals that she was in fact lying about everything.
After leaving the pawn shop, the evil Sally got to work on her fake kidnapping plot, first by tearing her clothes and then driving to the aformentioned cabin and shackling herself to make the bruises she had appear real. Part two of Sally's plan included returning to her home and killing Aaron by striking him with a two-by-four, and carrying his body and the rug it was on back to the cabin, making it look like she killed him there out of self-defense. Sally's motive: to get all of Aaron's entire estate. Monk reveals to Sally that he figured it all out due to the fact that she stepped on a chewed piece of Randy Disher's invented "Dishermint Gum," which Monk, while he was hypnotized, actually took off and chewed. Now that he was back to normal, Monk was horrified to learn that he had that gum in his mouth for over five hours and he tossed it down on the ground. However, since it was key evidence, both Monk and Sally wrestled each other to retrieve the gum. Once Monk regained possession, Sally demanded that he give her the gum back, but Disher and Stottlemeyer appear and arrest her.