She is an evil businesswoman who illegally poaches and shrinks protected wildlife in order to sell them to rich clients.
She is first seen in Africa, with her two henchmen, looking for animals that she can shrink and capture. Suzy, the protagonist, ends up being hit by Marilyn's shrink ray when she jumps in the way of her intended animal target. Marilyn takes Suzy back to her camp and intends to do her harm because Suzy has found out about her evil plans. However, the tiny Suzy manages to escape from Marilyn's evil clutches and runs off into the jungle.
Suzy later returns and intends to stop Marilyn from poaching any more animals. The two women end up fighting, with little Suzy even getting the upper hand for a moment, but eventually she gets hit once again by Marilyn's shrink ray and becomes even smaller than before. Marilyn captures Suzy and places her in a jar, telling Suzy that she will charge her clients a premium for her. Later on, Suzy's friend Frank appears, he is trying to find Suzy and seems convinced Marilyn knows where she is. Marilyn whips out her shrink way and shoots Frank with it, she captures him and places him in a jar as well.
Marilyn travels to London with the two shrunken heroes and visits the house of a wealthy woman. She presents the two tiny humans to the woman and tells her that they come with death certificates so she can do whatever she desires to them. Suzy angrily protests, telling the evil women that she is not a slave or an animal. Marilyn punishes Suzy for this outburst by shoving a pencil up her ass, this makes Suzy submissively apologise, and call Marilyn her master.
After this Suzy notices all the other tiny animals that the rich woman has around her house, she command them to attack the two evil women, which they do. Marilyn gets out her shrink ray and tries to use it on Suzy yet again, but is tackled by a tiny tiger. During all this commotion Marilyn is hit with her own shrink ray, but the setting causes her to grow into a giant instead. She loses all of her clothes and bursts through the building and out on to the streets of London. Suzy and Frank follow, and the evil Marilyn tries to crush them under her feet. Frank shoots Suzy with the shrink ray, the setting makes her a giant as well, and suddenly there are two nude giant women have a fist fight in the street. Frank shoots them both with the ray again, this time shrinking them, the two small women continue fighting with Suzy getting the better of the evil Marilyn, and causing her to give up.
A week later at a fundraiser for the African Wildlife Fund everyone is back to their normal size, except for the evil Marilyn. As part of her five years of community service she is made to dress as a Jester and provide entertainment for the party-goers. Suzy and Frank approach the tiny villainess and enjoy her humiliation, as Marilyn tells them they will pay for this.