So since Tang Qian died when she was just a little girl, that means that when she had that assassination mission (when she was already an adult) the one who actually saved her, getting gravely injured in the process, was Tang Zhu!!!
All this while Yao has been acting like its:
Tang Qian = an angel who saved her
Tang Zhu = a devil who bullies her
But it's really:
Tang Zhu = Tang Qian = both angel and devil