Speak with her and try to avoid the conflict

You force your voice steady,

"Wait, please. Before you decide my fate... hear me out. Only one minute of your time."

To your surprise, the Priestess tilts her head, sits down on a chair, and says "Speak, then, but choose your words wisely. You have ONE minute."

You plan your next move...
She's too powerful, and the place is crowded with guards.
You can say the truth and ask her to help you with the stone, or you can lie and pretend to be interested in the noble lord and his status.