Patralekha is not wrong in her place right now if she thinks she can break apart Sairat. She knows their relationship right now is at the most vulnerable state, one wrong move from either of them will break their relation forever.
Infertility is something very serious issue between couples, it has break many marriages, coz in our culture a marriage is ought to be fulfilled when couple gave a child, and failing to do so, it give rise to feeling of emptiness between couples and here Sai and Virat have known a fact that their family now cannot be complete naturally.
No matter how much love is between them, they are drifting apart, plus Virat's obsession with having his child naturally, plus his orthodox family who by hook or crook wants an heir, plus Virat Patralekha's history, his soft corner for her, family's inclination towards Patralekha, Samrat's death, family's disregards towards Sai, all this things are making Patralekha think that there's chance for her and logically it's not wrong too, she knows no matter how much Virat loves Sai, there will be nothing to tie them now and eventually Virat will get over Sai, if she gives him the happiness of child, coz afterall blood is thicker than water.
Hence, Patralekha is actually smart to grab this opportunity, as she said she has nothing to lose now, if she's unsuccessful, and if succeed than everything is her, which she always dreamt off.
Ps: purely my interpretation of her pyscology.
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