Hel is:
a) A deity.
b) Likely been plotting ways to end the world since shortly after the world began.
c) Knew votes would be coming up where the end of the world was a possibility.
I don't think it is a stretch to think she might have thought about it more then most people.
As a side element:
d) Had recently acquired a servant who had a stickler for the rules's knowledge of the rules.
The rules prohibit casting any spell on any creature during a council meeting (panel 8).Heck, theyre even aware of the possibility of outsiders screwing with the vote, because they have a barrier meant to stop non-dwarves from getting in, as well as a security team. Is it that hard for the cleric of Dvalin to cast a circle of protection from evil around the table before the vote goes off to make sure nobody has their free will violated?
They are - the vampire template does not remove the dwarf subtype from a creature who acquires it.