I like the turn this is taking.

Perhaps there should be some link between the Spiritual world and the mortal realm. Something along the lines of..

"When Iluq began her expansion of the ice from both poles, she found that even her massively augmented power could not both maintain the presence of the ice [b]and[/b] fight off the would-be defenders of the other kingdoms, never mind those who would oppose her from the water tribes. So, much as she herself had been given power by an ice spirit, she granted certain warriors under her control limited power over similar abilities, by way of 'blessing' them with spirits of their own, who in turn answer to Iluq and her own spirit. In this way, they would be strategically stationed in various locations around the world, maintaining the existence of the deathly cold ice. This would afford her limited omnipresence wherever her ice were to exist; she could sense whether it was still covering an area or not.

If those warriors were ever to be defeated and their powers drained, the ice of that area would rapidly recede, returning the land to it's previous form."

This would give the players clear objectives before going right after the 'big bad'. Areas covered in ice could be infested with water and ice spirits.

EDIT;
I'd also like to point out the potential for the involvement of other nations in terms of their military, the expansion of other plot points involving the spirit world, perhaps to the extent of the inclusion of other spirits who don't approve of what Iluq and her spirit are doing.