Emperor Rael immediately commenced the vetting process for Master Reina; not only did he instruct the deputy director of the Kandrian Bureau of Intelligence to vet her, but he directed the Kandrian Security Agency to conduct an analysis on her in addition to the one that he had tentatively conducted. He also arranged for Sage Farana and Matriarch Nephi to verify the sincerity and trustfulness of her intention to aid him.
She might have been an extremely impressive Martial Master, but she was unable to fool two Martial Sages.
Only then would he be truly able to trust her.
One of the reasons that he was able to execute his plans with extreme success was precisely due to his high levels of caution and veracity.
Regardless, he had reason to believe that he would be able to rely on her. While she had certainly played many pranks on Rui, she had never acted against his interests even when he entrusted her with extremely important duties.