The reason she recognized her was because Du Mengxin had seen Mu Xiangwan's photo a while ago.
On Su Chaoyang's last mission before being reassigned, he suffered some injuries. When she tended to his wounds, she was surprised to find a glamor shot of a girl in his pocket.
Later, she inquired about this with Su Chaoyang's comrade and found out that this girl was his love interest, and nominally his sister. The revelation was shocking– she didn't expect that Su Chaoyang could ever have feelings for a girl, especially one who was his foster sister!
She never imagined that after returning to Beijing, she would unexpectedly run into the same girl from the picture, witnessing such a spectacle.
Seeing that Mu Xiangwan already had a boyfriend and was so outspoken about fighting for a man in public, she felt an immediate distaste for the girl, feeling she was entirely ill-suited for Su Chaoyang.
