While Anna thought she had successfully deceived Kai, he was always watching her use the insects.
'Her personality makes her unique.' thought Kai. Anna has a lot of ambitions, but she lacks the qualifications to achieve them. She wants to avenge her family by killing Yang Wudi, but she does not want to risk her life in the process, and her determination is also not enough. But her two-sided personality is nearly perfect; she is a good chess piece.
'I should get rid of her after the completion of the plan; her ambition makes me unable to use her further in the future.' thought Kai. He did not want anyone to know about his involvement in kidnapping Yang Wudi until he was strong enough to protect himself and his family, so he needed to eliminate it to avoid any danger.
Kai did not immediately start the plan since there was no suitable location. Kidnapping the holy son of the sect is a pure death sentence, so he needs to wait for a perfect opportunity.