Alice isn't very fast on the uptake, is she? How many days was it between the moment she heard Sisbell propose her deal to Iska, and when she suddenly jumped out of the bath? And she's gonna trust her subordinate's plan, cause her last plan to kidnap him went so well?
As for Sisbell, in spite of the tunnel vision she seems to have developed in this chapter, she's still probably the best out of the three sisters to be the next queen. Unless the third sister, whats-her-name's secret isn't actually something dark and sinister like they've been implying.