At the beginning of the movie, Lena seems to be enjoying the high life with Koopa. However, when he finds Princess Daisy, she becomes exceedingly jealous of her, and fears that she is in danger of being replaced. After she finds the piece of meteorite needed to merge the two worlds, she tries to tell Koopa, but he ignores her out of anger. Lena then decides to take matters into her own hands, and attempts to "help" Daisy achieve her wish of escaping by killing her. However, her attempted assassination is thwarted by the royal pet, Yoshi, who attacks Lena to defend Daisy. He grabs Lena with his tongue and pulls her towards him as Daisy runs away, but before he can actually harm her, Lena stabs him with her knife and escapes.
When Koopa learns that Lena falsely told the troops that he had authorized the invasion of the human world to begin, he realizes that she has betrayed him, and still has the meteor piece. He has Lena arrested and the meteor piece is returned to him, but he drops it during his subsequent battle with Mario. Leaning over a railing, Lena manages to catch the rock; however, the railing gives way and she falls onto the wires below, electrocuting her and leaving her burnt and disheveled. Laughing maniacally, she rushes to the meteor and attempts to put the piece back in, despite Luigi and Daisy warning her not to. While completing the meteor does start the merge of the two worlds as she had hoped, it also creates a power surge so large that it vaporizes all of Lena but her bones, embedding her remains in the cavern wall behind her and putting an end to both her plans of universal domination and her life.