Becky first appears when the sea lions Fluke and Rudder call a flock of loons to help Marlin and Nemo find Dory. After Fluke introduces Becky to Marlin and Nemo, she starts pecking Marlin and Fluke tells her to bring Marlin and Nemo to Quarantine and Marlin is suggested to imprint by looking her in the eye and do a loon call. Underwater, Marlin and Nemo start making a plan about Becky and reaching above water, in which Marlin is curious to know which eye he should look at. One of the sea lions tells him to look at one of them in which by doing a loon's call, Becky puts Marlin under her while Fluke calls Gerald to bring a green bucket for Becky to pick up in exchange for letting him sit in their rock for a few seconds, but is soon shooed off by Fluke and Rudder once they declared that time was up while Becky carries Marlin and Nemo in the bucket to help find and rescue Dory in the Institute.
While being carried by Becky, Marlin is disappointed that Becky is confused and doesn't know where to find Quarantine and accidentally leaves Marlin and Nemo on a branch, thus she starts eating discarded popcorn along with a flock of pigeons that fell into a floor after Hank bumped into a girl who has a cup of popcorn while trying to get to the Open Ocean exhibit. Upon seeing Becky along with pigeons eating the discarded popcorn, Marlin and Nemo move the bucket and try to ask Becky to help them, but instead the two are launched in a tank with a toy fish resembling Dory inside by a gift shop.
Marlin and Nemo see Becky flying with the bucket at the top of Quarantine in which Marlin still starts calling for Becky to get her attention to bring Marlin and Nemo to Quarantine, but is unable to get help from Becky to rescue them.
Becky later appears on Hank's head during the climax of the film inside the Cleveland Aquarium truck when Marlin is calling Becky to return after a pack of sea otters retreat from one of the angry passengers that noticed the otters inside the truck. Despite Nemo and Marlin being rescued from the truck, Becky abandons Dory as Marlin tells her that he and Nemo need to be taken back to the truck again but Destiny, along with Charlie and Jenny, suddenly appear while Marlin is trying to get her attention. After meeting them, Marlin suddenly tells Becky to rescue Dory from the truck. She is last seen falling into the ocean in the green bucket, alongside with the other fish that are falling into the ocean when Dory and Hank (who hijacked the truck) drive the truck towards the ocean.
Becky later appears in the end credits where she tries to land on a branch within the Marine Life Institute grounds in which she suddenly falls off when trying to land because the "branch" is actually Hank camouflaged as a tree branch.