Lieutenant Ría Campos leads the FND squad guarding the PG-240X in the Mesozoico Special Operation. She carries the key you need, so she is the first target to find.
She is inside the Mesozoico map. Lola tells you about her at the start, then you track her down, kill her and take the key before going for the chemical weapon.
She is fairly weak in a straight fight because her pistol fires slowly. The hard part is getting to her past the squad. Tag her early and pick off guards around her quietly.