They've been capturing more slave ships on the high seas leaving Cheliax for Absalom, Katapesh, Taldor. They've also been missing more, because volume is up in general. The people of Cheliax are worried their government might ban slavery and the rich want to get even richer by condemning as many hundreds of people to torment and death as they can make a penny for. Andira despises them. She also despises attempting to capture the ships at sea. Slavers will throw slaves overboard, when they see pirates coming, so they can claim they carried only other cargo. They'll also fucking throw slaves overboard just because they didn't bring enough food.
Word has it that Cheliax is abolishing slavery soon. Very soon. All you need to do is stop them shipping every slave in Westcrown out before they do it. They have spies in Westcrown's harbor. It wasn't that hard; a lot of places were hiring, shortly after the war. They have solid suspicions about who's attempting to ship out slaves. Those ships just need to meet some unfortunate delays at port. A week's delays, to buy a couple thousand lives.
She doesn't go herself, of course. She is of Andoran; that would be an act of war against an ally. And Codwin's going to demand to know if she did it and she will need to be able to say that she absolutely did not, and would not have.
She just makes all of these observations in solemn council with her Eagle Knights and half a dozen of them do decide to go and do it.