Let's remember Soni, escaped death thrice already. Poor thing is an emotional wreck.
If you all remember correctly Taya asked Tayi when Moni left, what did Tayi say that made Moni sad that she left.
Maybe Soni did not word her her thoughts clearly (but then again she didn't get a chance), and then Mahi starts talking down to her older sister like that? Is that the way you behave with your older sister? If I ever dared do that, trust me I would have smacked right across my face. Forget older/younger, is that the way you behave with a guest who has come to your house? Even if you don't want people saying stuff about your family, there are better ways to say it. Words can never be taken back, and yes Mahi may repent, give her child etc.... but what she did was out of class, and maryada.
Secondly, Shabd. He knows that his Tayi has said stuff that made Moni uneasy, and he heard Taya say the same when Taya questioned Tayi, yet even he is turning a blind eye, and in a sense accussing Soni that how could she think that Moni was not happy in the Sareen house. Heck Shabd himself stopped Moni once from going.
If you ask me, Jeet was justified in his temper, and he is not creating differences as he told Soni if MAhi says sorry, forgive her, and end the argument.
However, if I was Soni, I would hesitate of seeing Mahi again, because of what she said. Heck the reason why Soni went to the Sareens was because her mother and loving sister were there. If the mother has left, and that sister considers Soni a stranger to protect her in-;aws, then what is the use of Soni going to the Sareens?
Funny how Mahi always used to say Jeet never took care of her sister when Soni was presumed dead, when Jeet did not know anything that happened, but he never talked back to her. Yet now when Moni has left the Sareens, and Soni tries to ask, Mahi is all defensive (even if she did not know what Tayo has done).
So all in all, Mahi like to blames and shout at others, but vehemently resents when she is tried to give a taste of her own medicines.
If she could not understand the value of her only living sibling, its a befitting punishment that she does not get forgiven.