The big difference between Sulochana and Savita ( apart from Savita's foul-mouthed behaviour) is more
fundamental.
Sulochana acts in the way she does to protect her daughter; not to harm someone.She does not draw any sadistic pleasure if her actions hurt someone else.
Savita , on the other hand acts purely with an intention of hurting and hurting badly to gain something for herself. She gets immense pleasure and satisfaction if her actions make other people (people she dislikes) miserable.
This is the big difference !!!