Born on an unknown date, Gilles joined the NCR Army at some point and was later promoted up the ranks to major. She was Boone's commanding officer in the Bitter Springs massacre in 2278. When NCR Army forces moved in to block any Great Khan members from fleeing the area of Bitter Springs, Gilles issued the order that anyone who tried to get past was to be shot on sight. What Gilles didn't know was that most of the Khans at Bitter Springs weren't the armed raiding force she believed was there, but women, children, elderly, the wounded and the sick.
Confused about what to do, NCR troops nonetheless opened fire, and Gilles froze up as the situation began to spiral out of control. Then-Captain Dhatri took command when he couldn't get a word out of Gilles, and did what he could to salvage the situation and stop the killings. For his efforts, Dhatri was promoted to major and placed in command of the 1st Reconnaissance Battalion. Gilles, meanwhile, was busted back down to captain and placed in charge at the very site of the massacre. No longer in command of an infantry unit, she was responsible for the refugee camp established at Bitter Springs, offering some safe haven to those displaced by an advancing Caesar's Legion.
If the Courier convinces Craig Boone to remain bitter and angry about the massacre at Bitter Springs, Boone eventually returns to California with his side-arm and two bullets to kill Gilles and later himself.
"About three years ago, this canyon was the main encampment for the Great Khans. NCR's 1st Recon tracked them here after a raid and made an attack. There was a communication mix-up that resulted in some noncombatants being killed. It was a tragic mistake, but we've done all we can to make amends."
"It started about six months ago. At first it was just supplies going missing - we figured it was refugees. Then people started dying. Always a single bullet to the head, always from extreme range. We've lost eight refugees and three soldiers to this son of a bitch. We know he must be hiding out in one of the caves up in the mountains, but I don't have enough men to send out looking for him!"