(responding to Rachel, stePH posted while I was writing) That makes sense. And it is consistent with the story. But if it's hinted at subtextually, well, it's done badly, given that so far, four out of four posters didn't get it, and I don't think any of us (with the possible exception of myself) is particularly obtuse.
It may be that this the fault of the reading, rather than the author. Maybe this story reads differently on paper than in audio. But the story as given - the story I heard - does not provide enough to justify the explanation given above.
Not to mention that the explanation does account for the main character's actions in the context of the assassination plot, but it still doesn't alter how mind-numbingly stupid the plot is. In fact, it makes it moreso - what was supposed to happen after the ambassador was poisoned? Was she simply to return home, touching no-one, and submit to her fate? Wouldn't there be an investigation anyway? Would anyone but an utter moron fail to connect the woman who showed up at the ambassador's door with his poisoning, and through her the priestesses? Why not poison him at the brothel, for that matter?
And as deflective pointed out, she could just have easily killed him with a dagger, given the lax security. Or she could poison his wine while her visited the brothel. Or if you feel like being fancier- as we know stray dogs are available - why not raise a poison puppy, and get the ambassador to pet it (or be bitten by it)? Note that the priestesses's plot involved waiting for a girl to grow into adulthood. That's what, 16 or 17 years of keeping your country under opression just to have a plan that could be easily stopped by a servent touching her flesh and getting sick en route to calling his master?
Anyway, this story - at least as presented in the PC version - layers thin, though consistent, character psychology on a totally implausible edifice of a plot. With a premise as silly as this story, even good psychological development wouldn't be enough - it would have to be utterly brilliant to make the story actually work. This story failed to supply that, by a long shot.