Kundan would have been released from that correctional school even without Mangala's doings.
Urmi would any way have been in danger because of Kundan.
But Mangala had an opportunity to save Urmi by reporting this incident and she lost it because of her andha pyar for Nimboli.
She chose to go with her superstitious belief over Nimboli in the face of real threat to Urmi's safety.
This is not the first time Mangala chose her interests over Urmi's safety.She did not want to take the helpof the social worker when Urmi was being abused because she knew along with Urmi Nimboli would also be taken away.
This is the second time she put her interests over Urmi's safety.
As for lying about Nandini's mother - Akheraj and Harki invented that story to save their skins and to escape from kidnapping charges. What made Mangala go with that story which Akheraj and Harki told?
She could have told the truth - same truth that she told Jagya - that she doesn't know where her mother is and she has not seen her and she cannot help her in finding her mother.
The child knows what big liars Akheraj and Harki are and she would have never believed them but instead she would have believed the truth about her real mother from Mangala and kept quiet
It is Mangala who is trapped in her own lies.