(Can you tell I'm catching up Podcastle? It's the one virtue of long plane flights.)
As with "Superhero Girl," this one disappointed me because the fantasy component was so understated as to be almost nonexistent. It really didn't show up until the last few minutes of this story, after more than half an hour of essentially mundane narrative. Well-done mundane narrative, mind you; my one technical complaint about it is that there was a stretch where it seemed like one sentence about the weirdo, three paragraphs about the sister's illness, repeat pattern. A bit too skewed of a balance for me, but fortunately it righted itself after a while.
In the end, though . . . the end didn't do it for me. As someone else said in this comment thread, you could remove the overtly magical element from those last couple of minutes and be left with 99% the same story. The rest of it is only "fantastical" in the way that (when I was a kid) From the Mixed-Up Files of Mrs. Basil E. Frankweiler was fantastical*. Imaginative, yes; what I'm looking for in a fantasy story, no.
*So this is where I hope memory serves me correctly, and there isn't any actual fantasy in From the Mixed-Up Files. Because otherwise I've just undermined my own point . . . .