Diana Peyton is the daughter of Hank Peyton and grand daughter of Jim Peyton and Grace Peyton. She is seen throughout the whole game but only in cut scenes as she is listening to her Grandfather's final story inside a cave that closed in and pinned Jim.
After listening to his story, Jim dies due to his wounds and Renard LaRoche is there grieving with Diana. They both exit the cave with Diana saying her final lines stating "what if we can take the fight to them? I have a plan."
After this, it is unknown to the player how her life played out and what she actually did to fight NEVEC and other hostile enemies.