Bai Qingyan still remembered that Xiao Rongyan once told her that the King of Xihuai had said he was not as ambitious as his little nephew. So even though Bai Qingyan had never spoken at length with Tuoba Yao, she knew that this child's heart must be filled with hatred towards the Yan Kingdom, and it's unlikely that this child would guard against his uncle, the King of Xihuai.
Moreover, for the kindness that Little Seven once showed him by saving his life, Tuoba Yao, despite being a prince of high status, willingly became Little Seven's guard, proving that he is a person of deep affections and loyalty.
