Selling your soul to talking mist (to anyone really) is probably a bad idea. Especially when it leads to being chased around a hellish battlefield by probably-demons while being cut to pieces by the air. But, come on. Kolasmenoe and her friend were about to die anyway, and she was not in the right mind to be doing anything other than running away from the whole situation. It didn't help that the mist was fairly pushy. Still. She could've haggled a little.