Wacky to think that, assuming she is who she says she is, that this chick read the protagonist's story about an entombed child carrying out murders in a specially-designed house and thought "Wow, that sounds like something my sister would do."
It's kinda wild how this entire story starts out with an androgynous occult journalist seeing a floor plan for a house and thinking "Gee, I wonder why there's a central room with no windows." Only for their architect friend to jump in with "Oh, that is what we in the biz call the abused child hitman room. It was the second most-desired feature amongst prospective home purchasers from 2015-2020 after granite countertops."
I'm kinda rooting for the ending here to have it turn out that there's nothing fishy going on and the whole weird room layout is because they wanted an extra bedroom but couldn't expand the footprint of the house because an addition would've encroached on a water main or something.