Even if you don't consider Vice Minister of Revenue Li Mingrui, the Left Prime Minister Li Mao was an important court official with many disciples. Any action against him would have widespread repercussions.
Once, Bai Qingyan broke Li Mao's youngest son's legs. She even sent Li Mao's subordinate's head to the Li Mansion's doorstep just to intimidate him. Li Mao understood that a warning could only go so far and refrained from further actions.
However, Li Mao's eldest son, Li Mingrui, seemed to be someone who disliked having leverage held over him. He believed he could be as ruthless as Du Zhiwei and adept at manipulating people, which is why he set up this plot.
He probably thought that Bai Qingyan ordered him to rescue Wang Qiulu. He then sent someone to inform her that Wang Qiulu had close ties with the King Liang's Mansion. By the time Wang Qiulu was sent to the Crown Prince, at least the Li family could stay uninvolved.
