Jane refers to herself as a "rebel slave" for revolting against the Reed family. In Chapters 1 and 2, she first steps into this role because she did not accept the harrassment she was experiencing. One of her cousins threw a book at her, causing the two of them to fight. Mrs. Reed holds Jane responsible for the fight, and wrongfully punishes her.
In the end of Chapter 4, when we learn that Jane had been accepted to Lowood School, we see her step into the role of "rebel slave" once again when Mrs. Reed tells Mr. Brocklehurst, the school's master, that Jane is a liar. Jane is outraged by Mrs. Reed's slander, and stands up for herself, ultimately telling the truth and how she feels about her.
While she is usually a quiet and obedient child, she was pushed past her limits, causing her to stand up for herself. Her dislike of injustice was greater than her need to sumbit to authority or any punishment she would endure.
