Everyone had secrets. Zhang Heng never asked how Shen Xixi acquired the Justice Scale and what sort of agreement she had made with the goddess of justice, Justitia. Shen Xixi, too did not ask Zhang Heng how he came to know about the location where Yogurt and 1810 would meet.
She and Black Swan had followed Zhang Heng here, subsequently managing to prevent two tragedies from happening during the critical moment.