Baa organized the puja for her son. It should be attended by everyone who loves and care for Vanraj - and Kavya is one those people.
Vanraj is a top-class jerk and Kavya matches him in everyway. But that doesn't change the fact that they are a couple now. Which woman will let her guy go his birthday party where his EX is all over?
Anupama can choose to either not participate in the puja or fight with Baa and not let the puja happen. She can't pretend that she is being forced to participate in the puja - she is strong enough to say no. She says all the time that Vanraj still has rights and relationship with his family. then she must give them space to get together to celebrate their own moments.
Anywayz, Anupama getting out of the way doesn't create any drama. So she has to be there.