Henina tends to irritate people. She can't help it -- she's bad at shutting her mouth. So when a prophecy is made that someone will stop the war, she figures she's the worst possible choice.
The Fates have their sights set on her, and it will take all her cleverness and quite a lot of offending the king to foist the prophecy off on somebody else instead.
But she can do it. After all, there are a lot of potentials to choose from.