Flex is first seen in the film walking down the stairs to greet Bond (under the guise of James St. John Smythe) at Max Zorin's château. After stating her name to Bond, he reacts in the same way he did to Plenty O'Toole in Diamonds Are Forever: "Of course you are." She then escorts Bond and his chauffeur Godfrey Tibbett up to Bond's quarters.
Flex is next seen at the reception party at the chateau conversing with Pan Ho and other guests.
Later in the film, when Tibbett is going to get his car washed at the local BP garage so he can telephone M about 007's discoveries, Flex and Pan Ho provide a distraction by pretending to have engine trouble while Tibbett gets the car washed so May Day can murder him. She next is seen while Bond is being disposed of in the Rolls-Royce.
When General Gogol and his men confront Zorin, his henchmen, including Flex, May Day, Scarpine, and Pan Ho outgun them, forcing them to leave.
In San Francisco City Hall, when Zorin has murdered W.G. Howe, Flex appears in the doorway with petrol canisters and begins to douse the carpeting so the building can be set aflame. After this, we see her walking out of the office with the canisters and then in the car looking at the destruction she's caused.
In the Main Strike mine sequence, Flex is seen patrolling the grounds and hands Scarpine the tool which leads to her demise: the dynamite (disguised as a coffee thermos) to flood the fault. After that, she assists in positioning the detonator Zorin intends to use to create a double earthquake, which would be utilized to annihilate Silicon Valley. Then after Bond and Stacey Sutton are discovered, she chases them with May Day and Pan Ho. After being directed another way by May Day with Pan Ho, Zorin decides to flood the fault before the personnel are evacuated, despite Bob Conley's protests. While the carnage ensues, the film cuts to Jenny and Pan Ho, who are about to be washed away by the oncoming floodwaters. Their attempts to outrun the waters prove futile, and they both drown.
Jenny's dead body is later seen floating in the mine as May Day and Bond are escaping. May Day grieves for her but Bond tells her there is nothing they can do.
- Bodybuilder Anita Gandol was considered for the role of Jenny Flex at a point when the character was intended to be even stronger than May Day.
- She is considered by many to be the true female villain of the film, as May Day changes sides.
- When Jenny introduces herself to Bond, he replies "Of course you are!". Bond did the same to Plenty O'Toole in Diamonds Are Forever.