Because in Paris (? Xiaolan and Shinichi saved Belmore's life (when she was chased by Akai Shuuichi dressed as a silver-haired pervert killer). ) Belmore tried to kill Xiaolan, but Xiaolan saved him when he was in danger. He didn't understand and asked Xiaolan why she wanted to save her. Xinyi said, "I don't know what the reason is for killing people, but do you need a reason to save people?" She was very moved and always regarded Xiaolan as her angel, which proved that God was smiling at her. In addition, she and Xinyi's mother used to be good friends and sisters, and probably didn't want to kill Xinyi. Plus, she likes watching the moment when the silver bullet destroys the organization (is it the abnormal psychology of cultivating the enemy first and then destroying it ...), so she doesn't intend to kill Shinichi. If Ai or Shinichi's true identity is exposed, she can't keep Shinichi, so Ai is also exposed to Shinichi's light and doesn't die.
The second question is supplemented, so as not to fight in vain.