Anandi's situation and Nandini's situation are totally different.
Anandi
Anandi was not kidnapped by Bhairon Singh and was married off to his son.
Bhairon Singh came to Anandi's parents with a marriage proposal and Anandi's parents accepted the proposal because they liked what they saw of Bhairon Singh.
Dsa was doing child marriage so were Anandi's parents and a lot of others were doing child marriage of their children.
Later because of the way Dsa was troubling her the little girl stole money and ran away to her parents.Her mother dragged her back and threw her at Dsa's feet and told her that this is her home and she has to live or die there.
Later for reasons like social security and emotional bonds she chose to stay on in BH.
Sumi and Bhairon treated her like daughter and they did Kanyadan because Anandi's father wanted them to do Kanyadan.
Shiv and his parents considered Singhs as Anandi's maika.
Anandi returning to BH had a seal of approval from Shiv's family.
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Nandini was not married off by her parents. She was kidnapped and was married off. So the marriage itself is not legal and it was made null and void by Anandi.
Anandi did not give away her child to Mangala or Akheraj as daughter or daughter in law.
Anandi's daughter landing in Jhalra was a result of a criminal act
Mangala claims that the child is her daughter,
So in no way are the situations similar.
Anandi's relationship with Singhs happened with the consent and approval all the important people in Anandi's life be it her parents, later on Shiv as well as his family.
If Anandi wants her daughter back she is right and if her daughter questions she has got good answers on this.