Totally agree with you. I can understand Veer's mom too. I say this with my own personal experience in fact.
My brother got married a few years ago, until problem didn't crop up between them, I was fine ,with my bhabhi,
meaning I was liking her But once she left my brother and divorced him saying we have compatibility issues, I felt I never liked her in the first place.... Thats why her bitter words to Mishti about she not liking her from the start sounded understandable to me.
And coming to the way she blamed and bad-mouthed mishti and her parents, she saw how much involved Veer was with Mishti. She saw how broken her son was after the breakup happened. Any mother would behave the same as she did. And why won't she bring her deceased parents in this, as parvarish will always been dragged in an issue like this and moreover her intention would be to hurt and humiliate Mishti as much as possible. So she touched her weakest spot that is her parents and their issues. She is wrong , absolutely... But it's human nature. I can understand where she's coming from.