What does Corlath have Harry do at the camp, why is she offended and what is Corlath's response to her anger?

Harry sees a broad grassland, with huge mountains and a small gap within them. She sees a small army on one side of the gap, with a few archers and several riders, and on the other, she sees a vast force of thousands. The small band, however, gathers up, and is led by a horseman whose sword gleams blue. A moment later, Harry finds herself back in the tent, with Corlath holding her up, looking at her with a sort of pity.