Mary only appeared briefly in the film when she gave Thornburg information on McClane and his family. Richard Thornburg was inside the news van keeping up with the Nakatomi Plaza Takeover when she presented a manilla folder in front of his face. Thornburg asked if she got anything on the McClane family when she responded by saying that she got his employment history and family address, which is located right there in Los Angeles. She gets a smug grin on her face, happy that she has found important information. They then left and drove to Holly Gennero's residence, but what they don't realize is that the information they put on television was ultimately seen by terrorist mastermind Hans Gruber, not only jeopardizing McClane's wife but also his own life and the lives of her children.
She was never seen again in the film, but her actions were done to further her own career without considering the consequences they could have. As a result Mary was fired and replaced by Celia as Thornburg's assistant in his next broadcast.