She is not. She just doesn't want an innocent baby to suffer. She hates what virat did to HER but she doesn't wish unhappiness, harm or bitterness on virat, shruti or the baby unlike people like BK, PP etc. She is clear she wants a divorce and she wants to get out the way. She does not condone or forgive his wrongs but she always knew their relationship was strange- she was a forced zimmefari on virat so Sai is just being mature enough to say- ok he loves this woman Shru so whatever- at least let him be happy with this family.
She doesn't want anything to happen to Shru and for virat to be left alone with a premature infant without even fanily support but she expects that his family will eventually despite their shock give in and help him care for ghar ka chiraag.
As of now she has no plans to be mahaan or stupid.
And I'm hoping that Shruti is killed so that it doesn't stretch anymore but sai does not become mother to random baby. Maybe if v begs her for forgiveness for hiding such big things maybe she can help take care of the innocent child but not as a mother for sure. When Sada comes back he can take care of baby.