In Bijoy's defence, he was very happy with their successful business setup in Kolkotta and was more than happy for Sona to let go of the Delhi arm. Let sleeping dogs lie, he told his wife. Then he got second hand information that his daughter and granddaughter are in potential threat from his ex-son-in-law. He intervened and that has not been followed up.
Instead, he now walks into a scenario where his daughter has brought the pride they lost 7 years ago back and his biggest fear of seeing her work alongside their nemesis has been put to rest. Only temporarily though. Because he saw, what he wanted to see - That his daughter did not find The Dev Dixit's presence unfathomable at all. Wait till Asha shows him what else there is to see. She has already clocked into the red flags twice now (once when she asked him if dev and sona were fighting and later when she witnessed Dev speaking to Bijoy).
So, I think in a roundabout way I am still saying what you ladies already said... It's all about perception management. Dev has stopped doing that while Sona has upped her game on that front. Till Ishwari didn't walk into her old place and saw the awards her son would win, she probably had a more modest visualisation of her son. Similarly, Bijoy had given up on their Delhi property and to have that back and to see Sona deal with Dev with such confidence would change his view of his daughter too
By not asking Bijoy to help her, she has already started making the same mistakes that Dev used to make - fake perception management