Kelly had entered the arena with her hands tied by principles. She wanted to fight off the horde without killing anyone, but when push came to shove, she was forced to make a choice. A choice that compelled her to trample her own principles under her feet.
When Kelly registered for the tournament she knew that she'd have to kill her opponents to progress to the next round. But killing children was where she drew the line.
Though the Deviants had lost all sense of reasoning and logic, in her eyes they were just helpless children suffering from an incurable condition.
As Kelly looked around her, she saw the whole arena painted red with the blood of the Deviants. Even her hands were dyed with death. The intolerable stench made her retch and she had to look away to stop herself from puking.