There are so many reasons to like Elizabeth Bennet. In Chapter 13 of Pride and Prejudice, she faces a very tough opponent. Her prejudice.  She is reading a letter from a man [Darcy] who has shown only contempt for her and in the letter, she is reading thoroughly damning charges against a man [Wickham] who courted her esteem very skillfully. You will admit that is a very difficult situation for anyone. It takes all of Elizabeth’s considerable strength to be willing to give the letter a fair reading, then to draw the conclusions she feels she must draw.
It is a letter that must be read the hard way.
We don’t really need to consider the case that is made. Let’s just follow the action as it unfolds. There is a commitment to fairness that lies behind all the exertions we see here, and an expectation of self control as well. She is amazing.
“With a strong prejudice against every thing he might say, she began his account of what happened at Netherfield.”
Although she begins to read with a strong prejudice; nevertheless, she does begin. When she has had all she can take, she folds the letter up. But she takes it up again because “it would not do.” That is not a judgment in favor of her comfort but a commitment to the possibility that these awful criticisms may have some merit.
“His account made her too angry to have any wish of doing him justice.”
She does not want to do him justice. Nevertheless, she does want to act in the ways she most values; to behave in accordance with her most important values. And that requires an attempt to do him justice even when she very strongly wants not to.
“…collecting herself as well as she could, she again began the mortifying perusal of all that related to Wickham.”
“…and commanded herself so far as to examine the meaning of every sentence.”
It is the attempt to do what she really does not want to do that requires the “collecting herself” and that effort produces the ‘command over herself’ we see in the second quote. It enables her to evaluate independently the meaning of each sentence. One at a time. Is it really possible that the case being made in the letter, a case by a man she despises, is credible even though it is about a man she is attracted to? That is what is at stake.
She put down the letter, weighed every circumstance with what she meant to be impartiality…
I think Jane Austen does us a favor here by admitting that Elizabeth’s attempts to achieve impartiality probably don’t get quite there. Austen says earlier that that Elizabeth’s feelings were so strong as to be “difficult of definition.” She couldn’t even say with confidence just what she was feeling; the strength of the feelings simply overwhelmed the categories she could confidently use.
Many of [Wickham’s] expressions were still fresh in her memory. She was now struck with the impropriety of such communications to a stranger and wondered it had escaped her before.
She remembered clearly the self-justification Wickham offered. Given that Wickham’s “countenance, voice, and manner” were so pleasing, she failed to give them the scrutiny she might otherwise have exercised. But now, reading and evaluating each sentence on its own merit, she wondered how it was that Wickham told her all these things given that they had just met.
Every lingering struggle in [Wickham’s] favor grew fainter and fainter..
Here we must remember that Elizabeth continues to struggle to favor Wickham. It is still what she wants. But she also wants to be in command of her faculties and further, she had a commitment to fair judgment. She realizes that she is exercising this commitment well after the evidence was gathered. She is demanding of herself the stringent examination of information she first accepted with simple credulity.
I have such admiration for Elizabeth. We have all been in her place, presented with information we wish to be false. We have not all—certainly I have not—demanded of ourselves the impartiality that costs so much. Why would I do that, we might say. Elizabeth doesn’t even ask that. She is committed to fairness and she understands that that commitment means nothing if she is not in command of herself.
 And, although this is not the pride of the title, she does say of herself in this chapter, “I who have prided myself on my discernment…”