I disagree, Sweety was totally at fault. She came across today as totally immature and insecure with respect to his son and the situation.
hosting a party for her sisters son, yes u need permission and you cannot assume it and go ahead with it. She asked and was forbidden .
you need not take permission to give a gift. How can Pinky guess that sweety would give him a bike. Knowing her as a person and sister for so many years, she was sure sweety wouldn't do anything against her character.
she wasn't able to afford that before and now she does and theres no harm in buying things you can afford, that does not mean showing off which is what sweety thought.
it feels like sweety is insecure of Pinky's status and her parvarish