I have a similar question, except mine is a little more complicated. I took on the quest to restore Princess Isolla of Suno to power in the Swadian Empire. Somewhere along the way, she got really mad at me because I gave too many fiefs to my lords and not enough to her and she joined the Nordic Faction......WHILE SHE WAS IN MY PARTY! I had a bit of a laugh, cuz anytime I award her a fief now, it belongs to the nords, but since she's in my party I can just besiege the castle and intimidate them into surrendering and re-award the castle.
Anyways, I finally took all the cities and hunted down the last of the Swadian Lords and I was successful, but upon the message that I destroyed the Swadian empire I get a message from Princess Isolla saying "NO STRING!" which I assume is a bug. What is she supposed to be telling me? Is the bug caused by Native expansion or just because she is technically in the Nordic faction or what? I'm planning on restoring another heir to power next....