The question: Can this word mean anything other than "sister-in-law"? Is there any other possible non-literal interpretation? ....Anything?
Someone told me that they thought maybe it could mean "foster sister", but they warned me that it was extremely unlikely (although that would make about a billion times more sense for the story). Is this possible?
If it helps, here's the complete sentence (and this is only sentence she's referred to in, sorry!):
The setting I would guess to be late 1700s or early 1800s England, although the narrative Japanese is modern-day.