She was played by Ashley Williams, who also appeared in Season Three of Warehouse 13 as the villainous Sally Stutkowski.
Darlene Coolidge is a "black widow bride"; before the episode's events, she had married two rich husbands under her real name and killed both of them, and she later killed a third husband after a five month marriage, posing under the alias Phyllis Gaffney. Darlene was being tracked by Randy Disher, then a sergeant on the force, but she got away.
Darlene later ended up in San Francisco under the name Theresa Scott, where she met Jonathan Davenport, Natalie Teeger's brother, and became engaged to him instantly. She was recognized by wedding photographer Frank Ruttle, who began blackmailing her; however, Darlene killed him in the early scenes of the episode. When she saw that Randy Disher was attending the wedding, the evil Darlene ran him down in her car in an attempt to keep him from identifying her. She also made an impression on Monk during the wedding dance; she threatened him while Monk was interrogating her. Knowing that Randy could identify Darlene, Monk gave a long wedding speech that kept both Darlene and Jonathan at bay while Stottlemeyer rushed to get the injured Randy mobile. Darlene was about to run off with Jonathan, but Randy arrived at the nick of time and identified her. Now exposed, Darlene held Jonathan at knifepoint and demanded a private jet, but she is taken down by Natalie. Though not shown in the episode, it is assumed that Darlene was arrested.