|The following is based on Fallout Tactics and some details might contradict canon.|
She is not in the game herself, but is mentioned by Simon Barnaky himself, his holotape, and some of General Dekker's debriefings connected to the case of Simon Barnaky's abduction. It is known that she shares the General's beliefs that the mutants are abominations that should be exterminated. At the end of game, when Simon Barnaky is revealed to be alive (even though not a human any longer), but became the Calculator's ally, it was the memory of Maria that enables him to stop fighting the Warrior and, if needed, take control of the Calculator himself.
Maria Barnaky was only mentioned in Fallout Tactics.