Lily Andrews was the hidden villainess from "Santa Claude," episode 7.11 of Diagnosis Murder.
She was played by Ann Gillespie.
Lily Andrews was the best friend of Sharon Basevich, but 13 years prior to the episode's events, Lily found out that her now ex-husband, Jonathan, was having an affair with Sharon. Lily turned heel in a furious rage and killed Sharon, stabbing her friend to death with a knife inside the Basevich home. After seeing Sharon's husband, Andrew Basevich, return home and finding his wife dead, the evil Lily knocked out Andrea and took possession of Sharon's earrings, keeping them in a safe deposit box. Sharon's husband, Andrew, was falsely arrested for the murder, but escaped and became a janitor at Community General under the name Claude Campbell.
Lily was interrogated by Steve Sloan in the episode, and she falsely claimed that she last saw Sharon at a country club two days prior to her murder. She also claimed that she was home on the night of the murder because a storm kept her from going to Sharon's, while pinning the murder on Andrew. After Jonathan stated to Steve that Lily's story isn't true, Steve returned to Lily's home with a warrant to search her safe deposit box, as Sharon's earrings were inside. Realizing that she was revealed as a murderess, Lily stated that she had to change her clothes, but in actuality, the villainess grabbed a gun and committed suicide.