I was puzzled at first, but after thinking about it a little, it seems to me that it's her adoptive family (and her real family died); Notice that when the elf asks her about her fulfilled wish, the girl is stunned. So she didn't know the wish was fulfilled, before the elf told her. And she only cried at this point too.
I can see how it can be interpreted in a different way though; She felt like she was cheated (because nothing happend) BUT a week later she sees the elf again, then she's stunned to realize she cared about her family, and cries while asking to revert it...
So, which one of these is accurate?
Well, the story is described as a story that gives you dark vibes, that can make you feel horrified without resorting to violence...
Where are the dark vibes if the story is a girl asking for her family to be killed, and they get killed?
If she regrets it, then the only vibes I'm getting is "Well next time I don't know, DON'T FUCKING ASK THE ELF TO KILL YOUR FAMILY?"
Nothing scary about that; As long as you don't wish for things, these things don't happen.
The only way I'm getting dark vibes is if the girl asked for her family to be killed, only to realize that other people she never met got killed (and she still has to deal with her adoptive family that treats her badly).
And at last: If it was the version with the delay... How is the delay explained? It doesn't seem to be explained mechanically, nor does it make much sense narratively. It just seems very random.
All this makes me think it's her adoptive family.
Perhaps someone reading the Japanese version could know for sure. Or perhaps after reading the other stories it'll be clear (just finished this one, haven't looked at the others yet).
Edit: But the briefcases kinda point out to her (current) family being killed. So I don't know about the vibes.
"Your family dying so you have to take care of yourself" doesn't really gives me bad vibes. It's something that's fully in the person's control, so if you don't fuck up, you don't suffer the consequences.
Not very scary. That's like showing a drug addict dying of an overdose. It doesn't scare me because I don't do drugs.