I've been through the untranslated version several times already without knowing what any of the words mean, and this moment in particular was one I always wondered about. Thanks so much for the translation!
When I just trying to go by visual context, I wondered if those red spots that he saw in Sia's mom meant that she had cancer or something, since they're reapers and all. The actual version is a whole lot nicer in that regard. But Sia's thoughts when she realizes she's not the one who can or cannot forgive, "she's already dead!" was an unexpectedly powerful moment.
It makes me wonder what the reapers' original plan was for when Sia goes back to her original body.