For Mauli, it would have been... Um how about not sleeping with her husband? Or not accepting his advances? It's not for Mauli. She did not ask Kunal to leave for Mauli she asked Kunal to leave "If he loves her", basically she wants Kunal to remember that he left her because he loves and when he goes back to Mauli, this is in his head that he loves Nandini.
Only if I wasn't sure that whitewashing is in the process, I would have been quite certain that Nandini is nothing but a vamp. Vamp has a motive and a reason, they are strong too but Nandini as positive as she wants to appear, she is coming out as a weak woman, who can't be loyal to anyone.