In case, like me, you are now concerned for this student's safety and mental well-being, my fellow English teacher tells me that the school makes a point of keeping an eye on her, so with this in mind, I marked the page with a big, friendly spiral (ALTs beware: in Japan, ticks are used to denote incorrect answers) and passed no further comment on what she had written.
(Incidentally, and as you've no doubt already realised, 死 - pronounced shi - is the kanji for death. Never let it be said that this blog isn't educational.)