uma, i think it would depend on the circumstances, when it was arushi's wedding she stood by her inlaws, and thus K when she declined to go, and if a situation arose again, she would try to be fair (i hope).
when it was the angad fiasco, she listened to her dad when she felt she ought to tell K the truth, but at that time she didn't love K, so that was what led to K's heartbreak and her face blackening sequence.
I think its his refusal to talk to her, even on the phone, and then his thumb on the divorce papers that has really rattled her, to the point that she didn't automatically obey her dad and go with K, she never contemplated the thought that her marriage would ever end, but then came KN with the divorce papers, and that's the shock she needs to come out from. That's why she remained silent with amma's drama going on, K didn't listen to her, but she felt what can amma do that could separate us, but she did so easily.
Both were at fault, K listened to his mom when he wanted to confront P about the money, etc, that was what P didn't know about and in the faceoff, P was shocked when amma mentioned that to her, that how could K believe i could stoop so low, that's what's eating her.