This scene from the novel shows Antoinette (Rochester insists on calling her "Bertha") confronting her husband. Let's put it this way: in Jean Rhys' book, Rochester is not a heartthrob.

"When I turned from the window she was drinking again.

"'Bertha,' I said.
"'Bertha is not my name. You are trying to make me into someone else, calling me by another name. I know, that's obeah too.'
"Tears streamed from her eyes.
"'If my father, my real father, was alive you wouldn't come back here in a hurry after he'd finished with you […] Do you know what you've done to me? It's not the girl, not the girl. But I loved this place and you have made it into a place I hate. I used to think that if everything else went out of my life I would still have this, and now you have spoilt it. It's just somewhere else where I have been unhappy, and all the other things are nothing to what has happened here. I hate it now like I hate you and before I die I will show how much I hate you.'" (Part 2)

Wide Sargasso Sea is a perfect example of counter-discourse, because Jean Rhys takes a text that is very important in the Western canon—Charlotte Brontë's Jane Eyre—and turns it on its head. This scene shows us counter-discourse in action. In Jane Eyre, Antoinette/Bertha is this crazy lady up in an attic. We have little sympathy for her, because, hey, not only is she crazy, she's also the reason that Jane and Rochester can't get married. She also (spoiler alert!) burns down Rochester's house at the end of the novel. In other words, she's made to look really bad in Bronte's novel.

In Rhys' book, Antoinette isn't crazy. We know that because we see things from her perspective. We see that she thinks that Rochester is a horrible husband. He cheats on Antoinette by sleeping with the house maid ("the girl" in the passage above). And he insists on changing Antoinette's name (Antoinette compares this to a voodoo spell that takes away her identity). And, because he is so mean to her in the beautiful cottage she thinks of as home, she comes to hate the place. Through Antoinette's voice, a different perspective is being presented here. A counter-discourse, in other words.

Even though this section of the book is narrated by Rochester, we see Antoinette standing up to him and fighting him. Rhys gives Antoinette a power and an authority that she doesn't have in Charlotte Brontë's book, and she does this by giving her a voice. In Jane Eyre, we never actually hear Rochester's wife speak. So just in showing Antoinette speaking up against her husband, Rhys is initiating a counter-discourse.