Mary used to live with her mother who was a famous dancer, but her mother died when Mary was young and Mary was left to another one of the dancers her mom worked with, Dominique Platt. Dominique and her two daughters, Britt and Bree, treats Mary as a servant/assistant. They all order her around making her do ridiculous things like "vacuuming the driveway" and "painting the pool pink" just to give her chores to do.
However Mary's life changes when she meets the teen pop star Joey Parker, also called "JP" by his manager and best friend Dustin. Mary and Joey dance together at the Black and White ball and Mary drops her "Zune" (iPod) and Joey make the announcement that he wants to return it if the right girl can name her top five songs. When Joey finally figures out that Mary is "the one" they become close friends and more so. Later on they split up for a short period of time because they are set up by the school's popular girls.
Joey holds a dancing competition and Mary's friends knows that she wants to enter, but Mary claims she is "done dancing" when the dancing school she applied to rejects her (she is not aware that Dominique interfered and made the school believe she had two broken legs). When Joey hears about the rejection he says he can change the school's mind to let Mary go to their school again and tells Mary's friends to just get her to the competition. Mary's best friend Tami along with Joey's friend Dustin tricks Mary to go to the competition and Joey manage to get Mary on the stage and have a "dance battle" with him.
After the show, which Mary won, a teacher at the dancing school Mary had applied to comes up and states "you dance very well for someone who has two broken legs" and Mary is accepted into their school in New York and finally she can leave the Platt house.
Mary is a shy girl, but very sweet and kindhearted. However she can have some snappy comments when Bree and Britt talk down to her at school. She does not really know how to approach boys when she likes them and mostly she does what she is told and does not argue. Mary does not really rebel a lot and rarely complains about her situation in the Platt house.
Mary has a slender figure with medium brown eyes and wavy brown hair. She wears tomboyish, baggy clothes and rides a skateboard. She is charming and sweet and works for a mean lady named Dominique Blatt and her step daughter's.