I think it's Shanti... Shanti will never never stop loving her daughter. She might pretend to be upset with her and may be even vent her anger, but will never every cut ties in the inside.
She wants to do this to show Ragva and the family how Mahan she is.
She wants the family to forgive Sarla, so that it doesn't look like she did it. This way when things go wrong again, she can say that "the family forgave Sarla" but I was Mahan and wanted to punish my own daughter...
it's all a trick. She want to make matters between her and her daughter so tense, that Kusia feels bad and mends the situation herself. Isn't that how Sarla got back into the house that last time? It think it was at Rakhee that Ragva forgave Sarla for the groom swap.