Maria only do what she says. If you choose the gentlest route you will see that she tries to be kind only to be scolded by Deborah. She is the bad influence that made Maria's mind. Maria is the weakest piece in this game. The real powers are the minister, the mayor, the police officer and Deborah is the money and Maria her pawn.
Again Maria is not a child. She knows right from wrong, Alright let me explain 'Hear Me Out'
What I'm trying to say is that. Maria went a decent enough age without knowing any of this, she went a good age without knowing Deborah, even if you want to make the case that she's weak minded which I agree with it's still not enough to Justify her.
She wasn't born in any violence at all, she lived a decent enough life to know what good and evil is, Weak minded or not.
Compare to someone who was born in the middle of Violence and doesn't know what the hell Good is a person like that is more understandable why they are so Violent and demonic, considering the fact they Born in the depts of it from day 1 so it's going to be Engraved in your head from a baby, but there's a difference when you know and do not know, weak minded or not.
(But anyways the way she was written towards the Plot is very understanding I Guess, anything can be written if you think about it OfCourse cause that's the main Point of the Story)
But from a 'Logical' point of view she knows good from evil.
Peer Pressure SUCKS I'll give her that though