Marlene was the fiancee of Stick Bernard and enlisted personnel on a fleet sent to retake Earth from Inbits. Both she and Stick were supposed to be married after their mission until her demise during the Second Earth Recapture Mission. While she perished in the first episode, her death has been the most consequential event for Stick Bernard.
Much of her previous life is not stated in the series, except for the fact that she grew up on Mars with her mother. She would begin a romantic relationship with Stick at some point and even served on the same ship, where Stick proposed marriage to her, as one of the bridge officers. Just before the campaign commences, she handed him a holo-pendant before Stick departs to the hangar. The entire liberation--just like the first--did not fare well as a large majority of the Second Fleet were destroyed that included Marlene's ship during the reentry. Stick--one of the few survivors--would open the holo-pendant that included her discussion on their wedding along with the dress she found at the boutique.