[ThereminVox]

Spoiler for Baseless speculah:

As others suggested, my first instinct was that she was very much alive, and was taking the role of the non-existent girl ritualistically. As for who her predecessor was, the girl in the morgue seems a good candidate. Which would make one wonder what happens to Mei after fulfilling her role, if that's really all she's doing.

Of course that's all speculation. She could just as easily be supernatural. But I like the idea that she's not because it opens up the possibility that the town's "countermeasures" for the curse may be more evil or unsettling than the supposed curse itself, and I rather like suspense stories of that variety.