Each of them were rt in their own space.
Dev - never understood that his mother liked going out with him. So its not the Saree that mattered but its the whole activity that she gets to do along with him . All these years he took his mom out because he didnt know how to buy a saree by himself. Todays episode shows that he has always wanted to buy one for his mom and surprise her like his sisters but never had the guts to do that because he felt he couldnt choose the best for her
Now you might think/argue, then how did he pick one for Sona . Well he is himself in front of her. There is no wall between them. There is no need to build an image of perfection in front of her because she has accepted him with his flaws. But when it comes to his family they look up to him and he can never go wrong.
Sonakshi - Poor girl doesnt know the reality . All she did was help him pick a Saree for his mom , whom she is slowly trying to give space in her life too... She to some extent understands the dynamics between the son and mom. But I am sure she didnt know the emotion attached to the task of picking a saree from his mom's point of view.
Ishwari - She becomes a child sometimes in front of her son. We have seen this before also when she fusses with food and her eating habit. And thats exactly what happened today also. She forgot that she is elder and is mother of four. Instead of taking a matured stand and respecting her grown up son's need to surprise her , she became a kid...