@eng1
The main daughter of a family is special, esteemed etc. but her family can choose to abandon her for her tainted reputation, being set up or not. And girls are just girls, if that main daughter is done for, then take another daughter! A concubine's daughter in influential family is still a daughter in that family, she represents the family's attitude towards the family she be wedded to. So yeah, in ancient Chinese settings, it's normal to do that.
@dabbingtool
It's not like anyone would believe her, or they do not want to get involved. Most people like to be bystanders watching some person that isn't them having her reputation ruined.
Also, you have to understand that ancient Chinese's women (or archaic women in general) were taught to always be obedient and faithful and kind and gentle etc, all the qualities to make a good wife. They weren't taught to defend themselves, physically or mentally; and good, esteemed girls always stay indoors anyways (or they have to dress up like men like Mulan or Zhu Yingtai) hence in their lack of experience in real life, so they won't know the basic knowledge we know when being sexually assaulted: to call for help and later take medical examination to prove you are still pure. Also, in ancient Chinese settings, men are more superior than women, so the society always takes blame on the weaker gender, saying "even if you are innocent, it's still your fault to be there to seduce a man in a confined room anyways!"