I just came across your comment and find interesting.
I'm not sure the exact situation that the old lady said that word, but it's used like "R.I.P" often, I think.
When is the book written, for I think the custom is quite old and no recent Japanese kid would be familiar with the word anymore.
When I was a child, I saw such case in animation of Japanese fairy tales.
Hope this would help you even a little.