Jie Yu didn't pretend not to know Du Youqian.
The body she had taken through Possession belonged to Little Sister Jie, the daughter of a disgraced official from the Wu Kingdom. When she fell on hard times, Du Youqian had saved her from the Music Bureau, sparing her the suffering of becoming a courtesan.
Therefore, she had once lived in the Celestial Master's Mansion and was well acquainted with "Master Baili."
When she later joined the Taihe Sect, she was honest about this part of her past, as the sect was extremely strict with its background checks for new disciples.
However, in her telling, she made a small alteration to the truth. She claimed that while she was presenting a dance, preparing to use her looks to entertain powerful men and climb the social ladder, "Master Baili" discovered she had a Spirit Root.
