She may have different set of values as compared to Akheraj and Harki.
But her attachment for Nandini is not natural.It came out of her own need for motherhood and wanting a child.She wanted that child because she felt her life is meaning less .
She endorsed that story that Akheraj told because it suited her purpose but at that time she could afford to be magnonimous and say that her mother must have had some majhboori in doing so when she knew all along the child was never dumped.Because it made her look more compassionate and also this helped in moving the child closer to her.The child would feel even if she is not wanted by her mother there is at least someone who cares for her.
Her bonding was based on this lie.
She told Jagya the story without thinking of consequences like she always does.As for exposing Akheraj it is the only good thing she has done so far and that too because Nimboli's life was in danger.
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Mahabharat war happened because of putr moh.People can go to any lengths in their attachment for their children.It may be mythology or it may be real but it still resonates because people connect with the emotions that drove the characters in that epic.There the father was not blinded because he did not of eye sight but was blinded by emotions he wanted his son to have what he was deprived of.
Here the lady wants the child of another woman because she has been deprived of.
Even now the child is more consumed by hatred for her mother rather than soothed by this mother figure.At least that should tell Mangala that the child is longing for her mother and she shouldn't hold her back.