Why is Jane Austen considered a strong woman?
Not a great deal is known of Jane Austen's personal life. She was born in 1775 and died of a lingering illness in 1817 at the age of 41. Her father was a member of the gentry, and served as Rector in the Church of England. She never married and lived with her family until her death. Very few of her letters have been preserved. Her most distinctive intellectual features are the ability to observe keenly and dispassionately and a lively sense of humor. She is also an outstanding literary craftsperson, both on the level of plot construction and language. Whether she was a "strong" woman is really unknown.
As you categorized this under Pride and Prejudice, we should note that Elizabeth Bennett in the novel demonstrates strength of character in being willing to turn down a marriage proposal from an extremely rich man on principle. She also displays strength in her ability to judge things for herself and not to yield to convention or powerful people, but instead remain loyal to her ideals, family, and friends.