Chelsea Patterson is a hidden villainess from "High Top Fade Out," episode 4.07 of Psych.
She was played by Ecstasia Sanders.
Chelsea Patterson worked at CyberVault, a company that encrypts data for other companies and the government, and was encountered by Shawn and Gus regarding the murder of Leonard "Diddle" Callahan, Gus' college friend and Chelsea's co-worker. Chelsea stated that Diddle had a crush on her and finally worked up the nerve to ask her out, leaving Shawn and Gus to conclude that he had been obsessing over her.
It was actually revealed that Diddle was investigating Chelsea, who was revealed to be using a security leak to give addresses of police warehouses to a drug kingpin. The warehouses had confiscated weapons, and Chelsea gave the info to drug dealers for a pay out. Diddle discovered Chelsea's evil double dealings, and as a result, he was murdered for it. During the interrogation and her arrest, Chelsea showed remorse over Diddle's murder, claiming that no one was supposed to be hurt. She agreed to give info on Diddle's killers as she was led away in handcuffs.