Some girls can pose naturally, and some cannot, but IMO, you should allow the model to "be herself" in as provocative as a pose as she feels comfortable. I doubt if she would have raised up her butt quite like that on her own, so maybe that is when the photographer just watches for the right pose, angle, frame, and light, and just lets the poses evolve as they will. If the model strikes a pose that is good but you're not ready, just ask her to "hold that" while you scramble to get yourself ready.
Also IMO, being more or less fully clothed can be very provocative and sexy. And some of the best pictures (IMO) are with the model posing in classy poses without being raunchy in any way.