I don't like the idea, but this feels like an analogous part of the story to the Goodsmoot of last book, and Elan learning about Tarquin's stealth empire in the book before that. Serini should, if not completely succeed with her plan, at least still be in a position to carry it out at some later point following her encounter with the party. It's just too big and looming a threat to pass easily, and I don't see a ton of room for intermediate outcomes between her whomping the party and getting stomped herself.