with her control over the spirits it would be stupidly simple to prevent the war, just have the spirits destroy all the weapons and armors in the kingdom, and to undermine the royals and the church, have the spirits deny all the royals and all members of the church the use of any kind of magic, even go so far as to make beneficial magic unusable on them, whenever someone joins the church they lose any and all magic they may have had before, if they leave they get it all back, this, at least is what i would do if i was her.
@TUSF
adopted or not, still wont change the fact that if the only heir dies, the kingdom will be in seriously deep shit when the king finally kicks the bucket.