What unconscious social commentary does austen's letter offer on pressures that limited a woman's choices in the past?

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.