Swamped

It's probably easiest to start with how the current situation is a problem for her.

"You know, they're going to be more than a little wary if I go to the temple and tell them I know they're keeping a sacred key at the training ground, and that some mysterious someone's aiming to get it. If I return the key you've got, and say I was given it by the person who warned me, they'll take it quite a bit more seriously."

"You don't have standing as a priest?"

"Of course I do!" you say insistently. "It's just... A number of my past reports were not considered important enough to act on. Enough that I may have an... exaggerated reputation."

"Who's circling the stone now?" she says, amused. "So you gave a bunch of bad reports and they're not inclined to trust you much any more, is that it?"

"No! They simply disagreed with my assessments."

"Sure they did. So what you're saying is, you don't have the credibility to deliver this warning. Well, if that's the case, then I don't see much use for you, so I might as well keep you in the cell and look for someone they will take seriously."

"No, wait!" you protest.

Too bad you were in such a hurry to object that you didn't think of what you were going to say next.