Diane Lance holds the rank of lieutenant within the Earth Federation Military's information branch. She first appears during the assault on the Alucard colony, initially posing as a refugee before her true role as an undercover military intelligence operative is uncovered. Operating from the Idaho ship, she coordinates communications and intelligence efforts, interacting with key personnel including Linda Plato and Soul Jirsett.

Captured alongside other survivors by Giganos forces following the colony's destruction, Lance is imprisoned aboard the Istanbul ship. During captivity, she demonstrates leadership by urging fellow prisoners like Linda Plato and Rose Pattenton to retain hope. She also clarifies tactical moves, such as the separation of prisoner groups, revealing her grasp of military protocols. After escaping captivity, she provides medical aid, tending to the injured pilot Kaine Wakaba.

Upon reaching Earth, Lance remains stationed with Soul Jirsett, Linda Plato, and Rose Pattenton during refugee disembarkation. Her intelligence expertise proves vital when she investigates an individual identifying as "Paul Coming" – later exposed as the Giganos infiltrator Meio Plato. Recognizing the security breach, she contacts military headquarters to report the impostor, triggering a base-wide standby alert against potential sabotage.

Though active in early and mid-conflict operations, Lance is reassigned away from frontline duties in later campaign stages. Her narrative concludes with a return during the series' ending events, where she marries Ben Rooney, the senior officer responsible for training the Dragonar pilots. This marriage formalizes their established close professional relationship observed throughout the conflict.