In 607, when Emperor Yang visited the submissive Qimin Khan of the Eastern Turkish Khaganate ("Tujue"), Empress Xiao accompanied him and she personally visited the tent of the khan's wife Princess Yicheng, who was a daughter of a Yang clansman. In 615, when Emperor Yang and Empress Xiao were touring the northern frontier, Qimin Khan's son and successor Shibi Khan launched a surprise attack against Yanmen Commandery in reprisal against various offenses by the emperor. Princess Yicheng sent the imperial couple advanced warning of her new husband's plans, and they were able to reach the well-fortified commandery seat at present-day Daixian in Shanxi. When Shibi Khan besieged them there on September 11, Empress Xiao's brother Xiao Yu suggested seeking further assistance from Princess Yicheng, who—pursuant to Turkish custom—was entrusted with overseeing military affairs at home in her husband's absence. She sent the khan a false report of a northern attack on the khaganate; between this and reports of numerous Chinese reinforcements rushing to answer the emperor's call for help and extravagant promises of reward and promotion, the khan decided to lift the siege and return north. (Subsequently, though, rather than listening to Xiao Yu's advice to end his campaigns against Goguryeo, Emperor Yang expelled the minister from his court.)