[She considers for a moment - again, the word isn't entirely nonsensical to her ear, but it's not anything that directly translates, either.]

We have "twin," although that's rare enough to be obscure. And we have "sibling" [- the word she uses is closer in sense to "fraternity brother/sorority sister" than the usual human sense of the word "sibling," the root word for things like "scourge sisters" or when trolls address each other as "bro."] but that doesn't imply consanguinity.