Well, temptresses are concubines and entertainers. They can get close to targets in a way that bruisers cannot (or ususally attract far too much attention getting to).
The real dilema is not setting up a plot that soley revolves around stuff that a temptress is good at dealing with, but rather making it something that isn't in the realm of what the thief can take care of.
Temptresses are great at the long con (sticking to a target to rob or take advantage of for a long period before finally tricking them) and they are good at the quick fix (seducing guards and dignitaries as distractions), but in the latter case, once thier cover is blown they are in trouble.
Just think of temptresses as a differnt sort of thief, set up a series of scenarios where bashing in and destroying things just isn't the best answer right away, and the temptress and thief will instantly become the most valuable PCs in the room.