The unnamed Murderous Wife is a villainess mentioned in "Mr. Monk and the Girl Who Cried Wolf," episode 3.06 of Monk (airdate July 30, 2004). She is the main villainess in Sharona Fleming's short story, The Fatal Recipe.
In the short story, the longevity of the wife's marriage isn't revealed, but as Sharona stated in the episode, the wife murdered her husband by poisoning his tomato soup. The villainess used carbolic acid to commit the murder, as it was untraceable--part of her plan to disguise the murder as a death via heart attack, though a motive isn't revealed.
The story played a pivotal role in the episode, beginning with Sharona turning in her story to her creative writing teacher, Meredith Preminger. Meredith turned heel after reading Sharona's story, doing so by using The Fatal Recipe to kill her own husband, Maxwell Preminger; using the same method that was utilized by the story's villainous wife. While Meredith ended exposed as a murderess and arrested, the fate of the villainess in Sharona's story wasn't revealed.