May be Nandini is not at all the way she portrays herself in front of others. May be she has a secret which no one knows. No one can be sooo dumb person. Nandini if really is, then should get an Oscar for been so dumb. She doesn't understands anything. Be it sarcastic, be it angry, be it taunting, be it sad, be it anything Nandini is always clueless. HOW?? WHY??
I guess its more to her character which CV's have decided to reveal in the end. My take on the possibilities why Nandini is like this are as follows. Feel free to add your POV.
Possibility 1
Nandini still holds grudges against Mauli for leaving her and becoming such a famous doctor and living a happily married life when she is living in hell decided to manipulate Mauli and shifted in her house. Then she decided to woo Mauli's brainless husband with her binidi, saree, blackless blouse and layers and layers of make up. When she knew this plan was working she decided to gain Kunal's sympathy and kept on crying in front of him. Slowly Kunal feel for Nandini and she got what she wanted, sleeping with Mauli's husband (not Kunal but Mauli's husband). Nandini knew this will break Mauli and her happily married life and her friend will become unhappy while she'll be happy with her friends husband. Nandini wants to marry Kunal now, thats how her Revenge from Mauli will be taken.
Possibilty 2
Rajdeep couldn't satisfy Nandini sexually and so she purposely distanced herself from him knowing Rajdeep would hurt her, Nandini purposely went through the torture so she could get free from this marriage but her plan got backfire and Rajdeep didn't left her so when Nandini met Mauli and understood Kunal is a great husband and satisfied Mauli, Nandini decided to sleep with Kunal and satisfy herself and she did. So Nandini fell in love with Kunal only to get satisfied everytime she wanted to have sex. (Sometimes people are in relation only because their partners are amazing in bed even if there is no love, the sex is good.)
Possibility 3
This is all Nandini and Rajdeep's plan. Rajdeep knew that even if he got the business deal with Kunal he could not make as much profit as he has imagined and with the help of his dear Mrs he enacts their horrible marriage in front of Mauli and Kunal. Believing it to be true, Mauli takes Nandini at her house and ask her to stay with her, Kunal and his family. Nandini as per her and Rajdeep's plan decides to woo Kunal and succeeds. This causes rift between Kunal and Mauli and they file for divorce. Nandini very well knows that Mauli will never ask for alimony and after Kunal and Mauli's divorce, marries Kunal and starts showing her true colours in front of him. She purposely makes false accusation on Kunal for sexually assaulting her and files for divorce and takes almost his entire property as alimony. Making Kunal a beggar, Nandini bails her dearest husband and they happily leave Mumbai with the alimony amount to start Rajdeep's clinic in their native place and finally live happily ever after with him, her husband, her true love.
Possibilty 4
May be Nandini is a psycho character. She just wants everything that Mauli has. And hence behaves in such a way.
Let me know what you'll think. I guess Nandini isn't and cannot be so innocent.