At the beginning of the movie, she works with her mom to con people of their money. Her mother also manipulates Mr. Bottle into marrying her. Throughout the movie, Mary-Lou and her mother treat Maria like a slave, just like the stepsisters do in Cinderella.
While bathing in the woods, she slaps Maria for touching her clothes. After the events of the Huntsman consoling Maria, Mary-Lou steals the white horse and rides back to Mr. Bottle's village. Mary-Lou gets hit on by a local cobbler, who made new shoes for her. She abuses him as a sign to leave her alone.
After seeing Maria singing to the prince, Mary-Lou steals her necklace and throws it down the well. Later on in the movie, the cobbler tries to get her to marry him, with the help of a local minister. When he makes Mary-Lou a garnet stone necklace, she wears it to the castle. She, along with the other rejected women, run out of the castle after a swarm of bees.
When Mary-Lou comes back, she offers to be nice to Maria and get her necklace, only to a point where Mary-Lou is manipulating Maria. When she comes back up, she steals the garnet-stone necklace that the prince gave her. Both girls end up getting sucked in to the Magical World of Mother Holle (another fairy tale classic).
While the girls were stuck in Holleland, they meet up to Mother Holle's house, and are forced to do chores, which Maria happily agrees to do. Mother Holle is a very nice woman. Maria happily cares for Holle's servants like a great mother. Mary-Lou tries to feed the babies, but one ends up peeing all over Mary-Lou.
When the girls get back to their homes, they get their "Just Rewards". Maria's clothes are transformed into a beautiful wedding dress and she gets her garnet stone back for her great efforts. As with Mary-Lou, pitch falls all over her clothes. As a sort of redemption (though one she is not happy about), she ends up marrying the cobbler, who tried to hit on her throughout the movie. With Maria, she lives a Happily Ever After when she gets married to a prince and they go to a castle. Mary-Lou does not get a happily ever after when the cobbler drives his carriage really fast and they crash into a pile of hay, showing that her future with her new husband will be a rocky one.