Nah, that can't apply here. If you are sending a kid home along a path you know will have a ritual going on that can't be disturbed, and a creature that can't be angered, and you aren't allowed to explain the situation, you can still say something to help prepare her. A cryptic piece of advice is also common in this type of story, but they didn't even give that.
If the rules really say you can't even give hints, then let her stay over for the night. Or make her go home before it gets dark! Or take her back yourself! Or don't let her come to your house alone in the first place! Or don't invite family to your monster-infested little village!
Anyway, on a re-read, it doesn't seem like the family knew much, if anything, about it. This is probably new to them, either it was someone else that set up the ritual or it was something the creature does itself. And it was the other kids who blamed her at the end, probably not the adults. They must have eavesdropped and discovered that she was indirectly responsible and misunderstood it as being her fault. And kids are stupid like that. Finally, it was her family, not theirs, that cut contact. Probably because their relatives live in an area with a monster.