I think Sai is at the point now where she is blaming herself because family's issue seems to be that Virat is prioritizing her over them and she feels guilty. She is getting affected by the taanas hurled at her because as Virats wife, having his family's approval and acceptance is now important to her. She wont admit it but she thats why she cares.
Probably she sees their behavior with pp and knows that if they can be SO nice to her, they are not "bad people" ALL the time, its only selective for her. And that probably bothers her a lot.
From her earlier stance of not caring about what they think, now Sai does care what they think about her- it pains her to on daily basis hear these insults and she is really hurt/broken by their behavior but she doesn't let it show. She did crumble bruefly- was in tears, down on her knees but even that didn't make bk gang tone down. But Sai wont let herself stay "weak" for too long. She doesn't know how to deal with it. She cant tell virat her pov because she feels like if he takes a very strong stand for her, it'll further alienate him from his family and increase his familys anger at her. She told Virat clearly today that if I give you all the details, your family will think its "kaan bharna". So she is dealing with it herself , trying to keep virat out of it.
Also as a naive person with heart of gold, her innocence still intact - Sai doesn't seem to hold too many grudges against these people and comes back each day as a new day. But every day they have new issue to blow out of proportion and insult her sadly.