A parent can be as bad as possible and a child can dislike them to the core but if that parent is hurt, all that anger goes away at the moment and all that child wants is to protect and help them. That was Roshni's reaction. She loves her father and mother for sure but it is her anger that gets the best of her.
Even in the beginning of the show Roshni had so much anger built up for her mom, but every time she saw DD in trouble and in any pain she ran straight to her and helped her in any way she could.
A child is a child to a parent and a parent is a parent to a child all regardless of how that child or parent is as a person.