However, Juqu Mujian also carried on an affair with his brother's wife, Lady Li, and Lady Li and Juqu Mujian's sisters carried out a plot to poison Princess Tuoba.
Emperor Taiwu, hearing that his sister had been poisoned, sent a number of doctors to the Northern Liang capital Guzang (姑臧, in modern Wuwei, Gansu), and they were able to save her.
In 439, Emperor Taiwu conquered Northern Liang, and took Juqu Mujian as a captive to the Northern Wei capital Pingcheng (平城, in modern Datong, Shanxi), but because of Princess Wuwei's sake, continued to honor Juqu Mujian as a brother-in-law with the title Prince of Hexi.
In 447, Emperor Taiwu suspected Juqu Mujian of planning a rebellion and forced him to commit suicide, but buried him with honors.
(Some historical records indicate that she married Li Gai (李蓋) the Duke of Nan Commandery,[4] but these are not conclusive.)