Early in the film, it is shown that Ellen does not get along with the cook, Mrs. Brill. By the end, however, she is shown to be much happier and gets along better with Mrs. Brill.
Ellen is first heard arguing with Mrs. Brill, which is so loud that Bert can hear them from outside. It is revealed that the nanny, Katie Nanna, is resigning from the position due to the naughtiness of their two children, Jane and Michael. In contrast to Mrs. Brill, who is happy to see her leave, Ellen unsuccessfully attempts to convince her to stay, partly because Ellen is required to care for the children when there is no nanny.
Throughout the rest of the film, Ellen is seen performing various household tasks for the Banks. She is charged with granting entrance to the various nannies that come to apply for the open position, and is puzzled when only Mary Poppins appears. The next morning, she is shown to be in a much better mood, getting along with Mrs. Brill and even humming during her work. Ellen later eavesdrops on George Banks' attempted sacking of Mary, explaining that she has heard the speech before. Later on, when Winifred Banks is looking for a caretaker for the children on Mary's day off, Ellen explains she is unable to perform the task due to certain chores needing to be completed. When the chimney sweeps invade the house, she is caught up in the mass and shown dancing with one of them.
Near the end of the film, the Banks are shown to be searching for Mr. Banks after learning that he had been fired. Ellen makes an offhanded remark about a certain bridge being popular with jumpers, for which she is chastised. She would be witness to his change of heart and watches as the Banks go kite flying.
Ellen returns for the sequel, played by Julie Walters. She first appears at the Bank's house as the sink burst out, and is extremely wet. She is the first to interact with the people trying to take the house, which she tells them to wait for Micheal.
She then appears when Mary Poppins comes into the Bank's house, when Mary Poppins says hello to her, with Ellen doing the same. She then appears throughout the film.
She then appears at the end of the film, when the Banks are leaving the house, she is going to stay with her sister, when Jane and Michael find the certificate of shares, and go to the Bank as Ellen stays behind. When they get the home back, they go to the carnival with Ellen and go into the sky with baloons and return home as Mary Poppins departs once more.