Shi has had a very pampered and sheltered upbringing. Dadu made sure that she lived in a bubble free of any troubles. In this bubble everything was shown to her as being rosy and optimistic. She never really had to face any predicaments or struggles as dadu made sure it was dealt with and never reached her.
Also she has always accepted the words at face value as that is what dadu had made her believe . So when people tell her things hence she just takes it blindly.This has made her always believe in what she saw and thats how her grew up. So her brain is trained to always look around and take that for what its worth . As she never had to analyze the situation over her too she has done the same.
She feels R is a traitor and greedy and everything about him is fake because of what she saw. Same with Abhi when he misbehaved she was angry but when he helped with Nishi she totally forgot the Abhi who broke her heart and also misbehaved.
I do understand that everyone is responsible for their actions and that she is not a kid. On the same note everything a kid learns in their childhood and growing up does stick with them and comes up at times of unrest. You do fall back to what has been taught to you.