From Halopedia, the Halo wiki
Mary is a member of the UNSC Navy and a crewman serving aboard the UNSC Spirit of Fire. In 2531, she was present for the Battle of Arcadia and the Battle of Trove. Following these events, she and the rest of the crew aboard the ship entered cryostasis, having sacrificed the ship's slipspace drive to destroy Trove. She was awoken in 2559 after the Spirit of Fire arrived at Installation 00.