Personally, I would say she wasn't hungry. I've seen friends snakes do what you are describing. They'll attack things in their cage, feeders, handler etc. out of defense. Once she's hungry she'll feed. From what I've seen in my snakes, and friends, is that if they bite and let go, it's a defense mechanism, like saying Hey! leave me alone! On the other hand if it's a feeding response to food they always coil.