The strory is based on tamil tv show. In tamil version Manav is svita's step son. Even in the Hindi version, description of savita's character says, Savita is Damodar's second wife and Manav's step-mother.though she feigns care and concern for Manav, she despises him. She camouflages her actual feelings as Manav is the sole breadwinner of the family. Not wanting any threat to her financial condition, Savita opposes any marriage plans for Manav.
If you watch beginning episodes, that's how they showed savita. In tamil version manav or his siblings doesn't know about savita being step mother until later. In tamil version sachin and savita creates lot of problems for manav and Archana. In hindi version they changed the story alot, death of sachin and kaka, second marriag, divorce crap.... My guess is, they started with original story in mind, savita has step mother then laster they might have changed it. Savita's character does fit for most of stepmothers..