There, Lucifer had gotten to her. She either needed to tell him no, mean it, and not keep flirting with the idea of sleeping with him, or she needed to sleep with him and satiate her curiosity. Of course, that option could prove dangerous, if she intended for it to only be a one time thing.
Lucifer waved and said goodbye, and then ducked out of the shop.
Really, Mary probably just needed to sleep with Kirk. He was certain the Captain didn't have the attitude and confidence to assume command at such a young age without at least something to show for it.