She was played by Kathy Baker.
Sylvia is a librarian at a prison where death row inmate Ray Kaspo was murdered—45 minutes before he was scheduled to be executed. As Sharona later revealed, Sylvia is the mother of author J.T. DeMornay, who wrote a tell-all book about millionaire Lambert Lawson. Lawson was suing him regarding the book, but his death of kidney failure kiboshed the lawsuit. After learning that Kaspo's organs would be donated to Lawson, Sylvia paid Tucker, one of the cooks at the prison, to poison Kaspo's last meal, which killed Kaspo and destroyed his organs. As a result, Sylvia was culpable in not only Kaspo's death, but Lawson's as well.
After the deed was done, the evil Sylvia killed Tucker to prevent him from talking, but Adrian Monk was on the case once Tucker's body was found. She sent Monk to interrogate Spyder Rudner (hoping Spyder would kill him), with a false claim that Spyder knew Kaspo when they met in Calgary. When that plan fails, Sylvia later sent a group of Nazi inmates to kill Monk, but he is rescued by Spyder. Though it is not shown or revealed, Sylvia is arrested for her crimes.