Julie is a human, from the planet earth.
Just before the start of the film, Julie had lost both her parents in a plane crash, blaming herself for their deaths. She plans on moving away to avoid the pain of no longer having them around.
Julie and Kevin are spending their last evening together when Kevin finds the Cosmic Key after it lands not far from them. Curious about the Key's origins, Kevin, mistakes the object for a Japanese synthesizer, and takes it to a friend at a local music store to get a second opinion. While the pair is separated, Julie is attacked by Skeletor's forces, and saved by He-Man.
Kevin returns to the school to look for Julie. The detective on scene, Detective Lubic, takes Kevin to Julie's house to look for her. Over the phone, Julie reveals to Kevin the importance of the Cosmic Key, but Lubic confiscates it, suspecting it to be stolen. Immediately afterwards, Evil-Lyn captures and interrogates Kevin, then leaves to acquire the Key from Lubic. Julie, along with He-Man and his comrades, meets up with Kevin and then proceeds to the music store. A battle ensues, during which Evil-Lyn, masquerading as Julie's dead mother, persuades her to steal the Key. Julie acquires it, and Evil-Lyn subsequently uses the Key's powers to open another doorway through which Skeletor arrives on Earth.
He-Man manages to retrieve the Key from Evil-Lyn, but Skeletor captures Julie and the others, during the course of which Julie is fatally injured by Skeletor's magic and the second Key is damaged and Skeletor threatens to kill them all unless He-Man surrenders unconditionally. He-Man gives in and returns to Eternia as Skeletor's prisoner. Kevin and Gwildor eventually manage to open a portal Eternia.
Julie, Kevin and Lubic watch as He-Man along with his friends engages Skeletor's forces in combat, during which he breaks Skeletor's staff, causing him to lose his newfound powers. Skeletor continues to engage He-Man with his sword, but is ultimately vanquished and sent plummeting into a deep pit.
After He-Man's victory, Julie is healed by the Sorceress. Julie and Kevin bid farewell to their new friends before leaving through a doorway back to Earth. When Julie finds Kevin, he confirms their shared experiences were not just a dream and holds out a souvenir from Eternia: a blue, marble-sized sphere showing the image of He-Man in front of Castle Grayskull.