Think about it. She has led a very sheltered existence and never been allowed to talk to outsiders.
When her family never let her talk to outsiders what makes you think they taught her not to talk to strangers?
Plus she is very trusting by nature. She is also very forgiving to the point a that she did not turn on NT until she realized NT wanted to hurt her baby and separate Maan from her.
NT and Dev were strangers to her alright but they were introduced to her by her family and so she trusted them. They broke that trust.
Maan himself was a stranger she met by the river and she trusted him, even in HP. Her family did not like him. But he saved her life. She fell in love with him and trusted him. She continued to love him even after she realized that he was Dev's brother. Because she believes in not judging people by other people's actions.
She trusted Meera and Meera might have been Dev's friend but Meera did right by her. She gave her a place to live and was her support during the whole MU track. In some ways Meera was the reason Maaneet reconciled because she advised her to apologize to Maan and that set the ball rolling.
Geet is rational and does not believe in judging a man by the actions of another. If that was the case she should have run as far away from Maan as possible after knowing he was Dev's brother. You may argue that by that time she knew Maan well and that is a valid point. Look how quickly she accepted NE and even forgave her after she caused her so much grief.
In some ways Geet is really innocent because she thinks the only person who will want to hurt her is NT. She is willing to give Arjun a chance because she thinks he is a nice guy. In her eyes Maan is doing him and injustice by kicking him out just because he is NT's brother.
So yes she is right in what she did from her POV.
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