The fact that Vivenna never really tried to get in contact with Siri is actually the easiest non-communication to accept for me. I can accept that psychologically Vivenna just didn't really ever want to, that she came to Hallendren more for herself than for Siri. After going to check on Siri in the Court, she probably realizes that whatever vague plans she may have had for switching places and recapturing her destiny just wouldn't work, and that's when she and the mercs really start to work on hurting Hallendren -- which I imagine for Vivenna had a psychological component as well.
Anyway I'm sure Denth would protest against it (no way to get a secure letter too her, Vivenna too visible now with the rumors to go back to the Court, etc.) and something could always be added to that effect. The mail thing is a good idea, too, though. I could also imagine Denth intercepting mail from Vivenna's father to Lemks and the spies...could be something that factors in later, or something else Vivenna sees along with the dead pets and dead Peprin.
With Siri...no matter what the personal relationship she had with her father, I guess I'd have expected him to say to her before she goes something like, "war is coming no matter what, and you need to use your position in the God King's Court to help us. You need to discover what you can about their attack plans, troops, line of command, etc., talk to the diplomats of other the countries, and report back to us via X diplomat or Y spy or using Z code." From a logistical point of view I understand this is tough -- Siri isn't a political animal a la Sarene, and too many scenes of her sitting in on the priest debates would be as boring for the reader as for Siri. Still, as things are now I end up feeling that Siri has been woefully neglectful in looking out for her home country.
MattD