I guess I thought, as others below did, that she spelled this way on purpose, to give the work a more old-fashioned feel. If her spelling is consistant than she must have written this way either because she thought it was correct, or because she was copying the style of older authors. I would imagine that the books that she had most access to were not the latest best sellers, but were decades old. If Samuel Johnson's Dictionary came out in (correct me if I'm wrong) about 1775, English spelling was still in the process of being standardized just 18 or so years later, when JA wrote these stories. We can see that some misspellings carry over into later works, most notably chuse. Whatever the reason, I find it charming rather than distracting.