Ansom did have one major clue where the wounded dwagons were. He knew that they were not in any of the hexes his units had already explored (the ones with known terrain in his map), and were necessarily in one of the unexplored hexes (indicated on the map as white "fog of war"). Ergo, he presumably sent Jillian far enough south to run a search pattern directed toward the hexes that were far enough away to be in the "fog of war" area, but close enough to be plausibly within reach for the wounded dwagons. From that area, her change of plans (from "performing the search" to "riding in to rescue the Fair Prince") would require her to "shoot up north".