Thorn sets out to get eyes on the enemy. She'd already seen their forces, but up to date information was important. In particular, right now, she wanted to see if she could find out who was commanding the tieflings. They should have some kind of sub-commander, someone who took orders from whoever the general here was.
Take that one out, and it might slow orders down and keep them from coordinating their attacks.
(Stealth [roll0] and Perception [roll1])