Based on her letter to her niece, Austen can't believe that her niece is truly "in love". Austen believes that her feelings were simply due to the proximity of the man and because of it, she can't say that she is truly "in love". She mistakes her emotions towards the man as something that is deeper, love.
Society during those times doesn't believe and allow women to think for themselves. They equate women, particularly wives, as extensions of their husbands and because of such thinking, society believes that women can't think on their own and must do her husband's bidding.
The answer that would best complete the given statement above would be option D. RHYME and C. METAPHOR. Based on the given passage above, Franklin used RHYME and METAPHOR to express a deeper truth. The words that rhymed are more and shore. Hope this answers your question.