I guess it's because she was too busy correcting Mr. Bose pronunciation of her name and Dev's name.
Any guesses on what her favorite dialogue is ...
"Mera beta itna sidha hai"
She can never accept the fact that her son could fall in love with someone because he is too innocent. Till now she only thinks that it is Sonakshi who has phasaod him and now that the Bose family has told her that Sonakshi fell in love with him first she confident of that fact.
I think she will be happy that he is escaped Sonakshi's clutches and only when she sees his suffering would she realize the extend of his love for her.