In 2008 (the setting of Grand Theft Auto IV), Roman's cousin Niko discovers that she is having an affair with Vladimir Glebov, but only because Vlad promised to settle Roman's debts if she had sex with him. Although Niko warns Vlad multiple times to stay away from her, Vlad blows off the threats. Eventually Roman sees Vlad's car parked outside of Mallorie's place and puts two and two together. Roman goes to Niko for support, but when Niko reveals that he had suspicions of the affair, it only makes Roman feel more upset and betrayed. Feeling bad about not informing Roman or doing more to stop the affair, Niko decides that it's time to deal with Vlad once and for all, and the cousins head to the Comrades Bar to put a final end to both Vlad and the affair. Although at the time Roman seems to want a peaceful solution to the problem and calls Niko a "hot headed chump" after he puts a bullet in Vlad's eye; later in the game he tells Mallorie that it was him, not Niko, that killed Vlad in a jealous fit of rage, and that Niko helped him dispose of the body. When Mallorie tells Niko this, he plays along and supports Roman's claim, and tells her that Roman is an "old school romantic".
During the Deal ending, Mallorie is left a widow (Roman was shot and killed while Niko disarmed and killed an assassin who inadvertently killed Roman while in a struggle with Niko) and tells Niko that the child will struggle without a father. Niko promises that her son "will never have to worry about anything."
In the Broker Safehouse, there is a picture of a much younger looking Mallorie next to the bed, in a picture frame.
Mallorie is known to smoke marijuana. She has a record of the substance, and there is a bong in the South Bohan Safehouse. It is not known if the bong is hers, however, as the apartment belongs to Mallorie's cousin.
The only time where she appears outside of cutscenes is in the mission Three's a Crowd.
She speaks with a unique accent that blends the stereotypical New York accent with a Spanish accent. The Spanish accent makes sense due to her Puerto Rican heritage, and the New York accent due to her upbringing in South Bohan, likely the poorest area in Liberty City (the New York accent is declining in use amongst middle and upper class individuals, although it has not been declining amongst the lower class as much).