^ agree. I don't think Preeti has the smarts or guts to pull off the stunts Sarla does. Sarla is just in another league.
Shanti is the main clever master, with Sarla close behind but also prone to bouts of stupidity. Pari is all bravado and stupidity but with bouts of intelligence. Nimmi is another Shanti in the making, but her morals sometimes come into the way.
Preeti's just dumb imo, not the next Sarla at all. She's always been this docile little lamb, pushed around by her family and silently suffering. And now she's stuck in this marriage and she's resentful. She's lashing out and refusing to see her mistakes. I don't see her as actively plotting against Riya like Sarla. I mostly just see her smirking and taunting for a long while.