@DigiTheMelon well the logical explanation as to why her lifespan change is either she was going to kill herself, or that the ability predicts that the protag will find a way to avoid the other girl's death.
I don't want to think it's suicide either but the 24hr countdown makes it tough to think of other options. This might be a bit of a stretch, but maybe death by grief? Or something like losing the will to live, not eating, etc. ? Maybe she just would have become zombie-like and mindlessly walked into the middle of the street or something. Idk I'll leave it at that, it was a happy ending after all
To everyone saying miss 24 hours was gonna commit suicide, the protag of this one shot has some pseudo magic ability which allows her to see lifespans. It's not unreasonable to assume miss 24 hours was under the effect of some curse or whatever.