What is Eddis not revealing in Conspiracy of Kings?

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After reading the book once all the way through and going back for infinite, infinite rereads of my favorite parts and many rereads of the detail in between, I think I understand that she has not revealed that she has already reached an agreement with the Attolias to cede her country to Gen... because of the prophetic dream about the volcano eruption that would destroy any possibility of the Eddisian people continuing their lives as they know it... but I'm not totally clear at exactly what Helen is withholding from Sophos... and exactly why she withholds it.

Can anyone offer me some clarity on this?