Yes she should've apologized but because he started off with the ajinkya thing she was already annoyed and not in the frame of mind to understand. I wish the ajinkya phone call had happened after Virat told Sai he was upset about her giving pendant and Sai had understood his feelings and apologized and then they could have had her explain her reasons and squabble about ajinkya when his phone call interrupted their conversation.
But here is Sai's pov- right now she doesn't know Virat loves her. For her, it was just a nice/thoughtful gesture but it wasnt perveived as a gift from "man to wife" by her. So she didnt feel as "attached" to it as Virat did. She did appreciate his thoughtfulness, his gesture immensely though as evidenced by her reaction on getting the gift. In her eyes by giving it to bk and ending the drama, she was showing her maturity and was trying to show her apnapan towards Virats family. Sai right now is in the frame of mind where she is craving acceptance from the family because they are important to Virat. She thinks that if things are better in CN, Virat will also be pleased with her. In future hopefully when she does have realization of love, her priority will hopefully change to Virat first and she will better understand the husband-wife dynamics. Right now she thinks family has first haq on Virat and more haq than she does. She thinks she is just a responsibility on him that hes nice and considerate enough to fulfil because hes a righteous and good man who regarded her father very highly and promised her dying father to take care of her. She knows she is safe with him, feels an attachment with him, and can trust him like a guardian to take care of her and support her, in return she is grateful and also wants to do everything to take care of him and his family too but she has trouble nabigating the waters of their atypical relationship. She has not even entertained the idea of loving each other.