At the beginning of the movie, Lena is enjoying the high life with Koopa. When he finds Princess Daisy, however, Lena becomes jealous and fears that Daisy might replace her (though in reality, the princess wants nothing more than to escape).
Later, Lena finds the piece of meteorite needed for Koopa's plans to merge their world with Earth - but when she tries to tell Koopa, he is too angry to listen. Lena decides to take matters into her own hands, commanding Koopa's troops to invade the human world on his behalf. Later, she attempts to kill Daisy to "get [Daisy] out", but is thwarted by the royal pet, Yoshi. Daisy runs away as Yoshi pulls Lena toward him with his tongue, but Lena wounds him with her knife and escapes. Koopa soon learns that Lena betrayed him and made off with the meteorite; he orders her arrest, and the meteor piece is returned to him.
However, during his later battle with Mario, he drops it, and the escaped Lena is able to catch it while leaning over a railing, but the railing gives way as she falls onto the wiring below, electrocuting her. Lena survives, severely burnt and laughing maniacally as she rushes to the meteor to reinsert the missing piece in spite of Luigi and Daisy's warnings. As she completes the meteor, the merge of the two worlds begins - but the act creates a massive power that vaporizes Lena, with the blast embedding her skeletal remains in the opposite cavern wall.