Poor girl. She kept on getting into misunderstanding after misunderstanding despite her genuine feelings and regret for not expressing it.
She could spiral into a mental feedback loop, in all honesty. She liked him, so she should've acted on any single opportunity to talk to him. He liked all his classmates so surely he's receptive of her keeping him company. Even if it's not romantic, a friendship between the two could blossom. They could go to school together, hang out, and get to know each other better. They could help one another, lend an ear, and be a shoulder to lean on in times of need.
In times of need... huh? Yeah, especially when the anemia kicks in.
She already saw him in that very incident. That meant there was an opportunity to get near him, say hello, and actually see and catch him as he felt the dizziness kick in. So why was she just standing there watching it all, assuming that he jumped of his own volition?
The simple opportunity of interaction that had been continuously being placed in front of her could have been the very thing that will save his life, had she followed up on even just one of them. And she did not act on every single one, letting hesitation half-ass her decisions. She only wallowed in his death, spun a story out of her own self-loathing and projected it into the ghost of the boy who already died, and destroyed his body further after that very fact.
It's not her fault, yes. Nobody could have known. But she already said her wish. That should have been enough reason to even half-ass an attempt, and still succeed. There was every reason, will, desire, and chance to make life better for the both of them, yet it was she who did not take it.
So she stands there in shock for splitting the ghost of her supposed crush in half, slowly trembling perhaps from the fact that she had misunderstood everything once again.