I'm also betting that she isn't a ghost but MC just assumed she was, because unlike spiritualist girl, MC wasn't able to hear ghost voices before:
https://mangadex.org/chapter/897269/1
https://mangadex.org/chapter/902000/1
Is she even a ghost at all?
Reminds me of the news story about a Japanese man who discovered that a homeless woman had been secretly living in his closet for a year.
... come to think of it, it's a bit too similar, I wouldn't be surprised if this closet squatter was based on that story.