How does Brontë present Jane and her principles in the novel as a whole?

Bronte presents Jane as person guided by her principles, especially her sense of justice. From the earliest part of the novel, we see the young Jane as a person deeply upset by unfairness. She does not understand why she is often abused, even if she is a poor dependent relative. In the opening pages, she strikes back against her cousin John's nonstop bullying. When she is locked in the Red Chamber, she thinks it is  

Unjust!—unjust! 

Later, she is deeply hurt and angered when Mrs. Reed unfairly labels her as a liar to Mr. Brocklehurst. She feels she "must" speak to her aunt, and she says: 

I am not deceitful: if I were, I should say I loved you; but I declare I do not love you: I dislike you the worst of anybody in the world except John Reed; and this book about the liar, you may give to your girl, Georgiana, for it is she who tells lies, and not I.

At Lowood School, Jane is angered by what she considers Miss Scatherd's unfair abuse of Helen Burns and can hardly understand Helen's patience and endurance under the injustice. Jane says the following to Helen:

And if I were in your place I should dislike her; I should resist her.  If she struck me with that rod, I should get it from her hand; I should break it under her nose.

When she finds out that Mr. Rochester is due to marry her when he is already married to Bertha, Jane's sense of fairness is again hurt and outraged: Mr. Rochester deceived her. It was unjust to morally compromise her by turning her, in essence, into a fallen woman living unmarried to a married man. Although Mr. Rochester tries to explain that he loves Jane, Jane's principles are so strong that she flees even though it means facing danger and poverty. She is willing to face hardship and even death rather than compromise herself and stay with someone who has deceived her.
In all these cases, we can see that Jane is willing to stand up for herself against injustice, even if it costs her personally. Her personal integrity is her strongest trait, and she is unwilling to compromise it.