I've heard of infection sometimes being the cause, Heather, often from a grass awn or other type of seed that got inhaled and stuck. It's not that uncommon in hunting dogs cuz they're always using their noses. That's why vets usually recommend the rhinoscopy and flush. Although most of the people in this thread weren't that fortunate, I'll say a prayer that Katie falls in the lucky category!
Good luck tomorrow! I'll be keeping you in my thoughts and prayers. Please keep us posted!