"When we got to Vegas, there were only sixteen people here...they were waiting for him [Flagg]. When we got into town, Jenny Engstrom got down on those pretty knees of hers and kissed his boots.
"I bet she never told you that in bed.” He smiled crookedly at Whitney.
Jenny is assigned to work the cherry-picker on a street-light maintenance crew. She becomes coworkers with new arrival Dayna Jurgens and befriends her, unaware that Dayna is spying for the Boulder Free Zone.
Dayna is exposed in little over a week, whereupon Jenny becomes cold and hateful to her — though Dayna perceives that Jenny is still not actually a bad person, and does not even wholly believe Flagg's propaganda about the Zone. Rather Jenny, like her lover Whitney Horgan — like many residents of Las Vegas — is just terrified of Flagg.
Dayna manages to commit suicide without revealing any classified information to Flagg. That, along with other factors, convinces some of Flagg's followers that his control over Las Vegas is slipping. Jenny is named as one of a small party of defectors who plan to "cut and run" to South America.
Before the defectors can leave, Larry Underwood and Ralph Brentner are captured by Flagg's pickets; by his order, they are scheduled for a public execution by dismemberment. When Whitney condemns the crowd for allowing things to escalate to this barbaric degree, he is mutilated by Flagg. Jenny is in the front row of the crowd, "whey-faced", and does not join Whitney in his denunciation or leap to defend him.
Moments later the Trashcan Man arrives, hauling a nuclear warhead out of the desert and into the assembled crowd. The ball of energy summoned by Flagg to attack Whitney transforms into the "hand of God" and detonates the weapon, destroying Las Vegas and vaporizing everyone at ground zero.
However, there an uncredited extra in the scene where Nadine Cross plummets from the balcony of Randall Flagg's penthouse suite; at street level this female character, wearing a hard-hat, reacts in horror to Nadine's death.
The same extra is later seen hosing down the blood-spatter from Nadine's fall; "Jenny" is mentioned explicitly by the actor playing Whitney, who glances towards her.