[Maltrease]

I think Norfleet means that since you have a force capable of defeating the vampire queen you are conquering territory and assimilating the fortress. The vampire queen by itself will not be able to retake the castles. So even though the VQ is coming back every turn they are still losing ground against you.

I can see this applying if your invading army was created in a way where you are not taking any (or only a few) losses against the VQ.

The vampire queen would need to be naked or they would be losing a lot of equipment every time they are defeated. I imagine it wouldn't be that difficult to defeat a naked vampire queen with the right force without taking many losses.

10 lighting bolts on the first round ought to take it out since the defender gets to go first?
Of course if the vampire queen was accompied by 20 vampires the story might change a bit...