The fact that Captain Lain was helpless to stop the creature because her power was insufficient devastated her. Many people died, and she was powerless to intervene.
She knew it wasn't her fault, but maybe, if she had been stronger, at least she could have saved someone. Despite her training and strength, she felt helpless against the gigantic creature, and once she thought again about the horde of monsters marching toward the city, she felt depressed.
There was basically no way to stop the horde from marching toward New Alexandria, and it was less than a week away. The beast was still alive but now too weak to escape death. If the thaid tried to escape instead of attempting to kill the humans, they wouldn't be in this situation by now.
The beast was still trying to fight at that point, but it was clear that there would only be one outcome for it due to its blood loss. A few seconds later, the warriors surrounded the animal and attacked it mercilessly.
