Rahm, unfortunately people like Arushi do exist. They put some stranger (one with whom they do not have enough intimacy) above their own loved ones. They will believe anything that person say and disregard anything their own loved one's say.
I can only think of two reason and that is insecurity and or possessiveness. Insecurity because they think this is the only person for me, this person loves me and fall for any trite words coming out of that person's mouth. The second is possessivenes, their own feeling is too strong, stronger than the other person concerned. So they will cling and hold own and put their own spin on whatever they say or do.
I think Arushi to some extent is like that. She is not so accomplished like Pratigya and may feel insecure. Everyone in the family listen and do as Pratigya say. That must create some sort of complex in her, to the extent she would want to show up P. I believe this is what the Cvs intend to show.........It is all natural, siblings to harbour these kind of feelings....