She and she have disliked each other since childhood, but unexpectedly they have the best tacit understanding.
When the apocalypse came, she and she became the best combination on the road to survival.
But one day, she was scratched by a zombie. She knew that she would not kill her, so she found an excuse to trick her away.
By the time she returned, she had committed suicide.
She was so distraught that she stabbed herself in the heart with her suicidal dagger.
Then, everything resets to zero, and she and her story start from scratch.