Seeing Celine nod her head, Denali explained. "That's right. I was looking for all the information about the one that had the intention of having him killed. I just arrived tonight and he thought that it would be good if I could find the information that I could tonight."
With Denali's ability to detect the loyalty of people towards Jack, she wasn't worried that Celine would actually reveal the information that she was giving her.
As a precaution, she had already made sure not to mention things like; they had already found who it was behind the incident and so on. After all, although Celine might actually not betray Jack, who could guarantee that she couldn't talk to one of her friends about it?
And once the friend knew that Jack already knew who it was that had sent an assassin, maybe that friend was actually amongst the spies that were sent to keep a tab on Jack's location.