It is never easy for a victim to come around what happened with them and it was understandable that Sonu did not want to create a ruccus until she got married or just after her wedding.
But but but, the show at various occasions has pointed out how Sonu never stands up for the right cuz she is that timid (or whatever adjective you'd like to give)
Occasion 1 - During the Jagrata Ep, when the guy was about to touch the girl. It was both Sonu n Ishqi who were a witness to what happened.
While Ahaan misunderstood Ishqi thinking she pushed the guy, creating a scene at the Holy Gathering.
Sonu, knew that she didn't push him but the guy was so drunk that he tripped himself.
Sonu didn't utter a word when Ishqi was being taunted by Ahaan on her upbringing and what not. It was much later in the night (after things had settled) she told Ahaan about it.
Occasion 2 - The famous Baba ji/Havan episode. The entire family shun Ishqi and her thoughts while it was actually Sonu doing the talking. Ishqi was humiliated right left n center.
Sonu, did not say a word. It was dadi who knew that it was actually Sonu who was talking. Ahaan this time was very infuriated by Sonu not owning up for her mistake.
Occasion 3 - This time, a lot was at stake for Sonu. Yet, she could have found a way through it. To tell atleast her brother about it. If not immediately then after a few days of her wedding and ask him to break all ties with this man Mayank.
But neh!
I hope Ahaan really throws some brain to her for keeping her mouth shut for so long and making Ishqi a scapegoat for that freaking long.