After watching didi's true face mishri had said to Didi that I was going to leave you and raghav but now I won't leave you with him.
I think now vaani is using this against mishri to gain her trust back so that he she leave raghav. She is pretending that how good I'm. She is just trying to win mishri's heart by becoming good.
She tried a lot to seperate them but couldn't get succeed. So this is how she'll try to seperate them. I'm sure it will be didi's plan to bring daadi on road.