Yao Mengxian smiled at her second sister and used a handkerchief to wipe the tea stains from her mouth. She didn't think her second sister was helping her; it was more likely she was afraid they would quarrel here and lose face before the Princess, thereby disgracing the Duke Mansion.
This second sister was always one to protect her own interests, being the legitimate eldest daughter of the second house and Yao Mengdie's biological sister. To Yao Mengxian, this sister was already the only person in the mansion who harbored no ill will towards her.
It's not that Yao Menglian would help her; rather, Yao Menglian wouldn't hit someone when they're down, and unless her interests were threatened, she couldn't be bothered to intervene.
