T2 Trilogy timeline
Mary and her son Kyle were captured by Luddite Patrol A-36 under the command of Sam Marshall AS-783490 and delivered to a Century Work Camp to serve as slaves. Dennis and their grandson John Connor led an assault against the Luddite extermination camp three years after Mary and Kyle were captured. Mary and her husband were killed by a Terminator during the assault on the camp.
Terminator Genisys timeline
In the original timeline, she was killed during the War against the Machines. The couple used to tell their son about the live before the Judgment Day.
Mrs. Reese is alive in an alternate timeline, where she, her husband and young Kyle were called to the police station. The Reese family were asked if they knew the man, the older Kyle, inside the interrogation room. None of them knew him, just feeling the man looks familiar. She said the man looked much like her husband. After a while, when the police station was attacked by the T-3000, Sarah helped the family to evacuate from the scene.
- Mary Shea is an Irish according to the film Terminator Genisys. It is unknown if the crew of Terminator Genisys has checked the origin of her surname, which is actually from Ireland.