Well, exactly, we can not reach a conclusion based on unsufficient evidence. While you argument is true, bare in mind probability and the relevence of the matter.That's theYou must be registered to see the linksfallacy, the fact that nothing has disproved the possibilty that Jill is adopted does not suggest that she is. There's no proof that she isn't Canadian either, that doesn't mean she is.
We can dismiss Jill being a Canadian, simply because it holds no importance to the story. Hypothetically, might as well be of any rase or etnicity given the probabilities and the relevence tp the story.