Wonderful post and protest!
I agree that Payal should have refused the wedding. However that she could not is a testimony of how regressive society is, even in this day and age, especially in small towns, such as Chaibasa.
As you point out, the title is SWB, not Service Wali Ladki or Service Wali Beti, and therefore the marriage had to take place for the story to unfold. I hope that Payal grows to realise that she has made a big error of judgement in going through with this marriage. Understanding this will be a good development of her character and will be the starting point of her redemption.
I hope that Payal does not try becoming mahaan and attempt to win over the family with her goodness. It just will not work, as the Prasads are made of sterner stuff. They may all act loony on the surface, but we have seen the dangerous undercurrents of avarice and violence behind the comic facade, adn they can go to any lengths to get what they want. Payal should therefore have a healthy respect for who she is dealing with and proceed cautiously.