"I had my own reasons for being dismayed at this apparition; too well I remembered the perfidious hints given by Mrs. Reed about my disposition, &c.; the promise pledged by Mr. Brocklehurst to apprise Miss Temple and the teachers of my vicious nature. All along I had been dreading the fulfillment of this promise,--I had been looking out daily for the "Coming Man," whose information respecting my past life and conversation was to brand me as a bad child for ever: now there he was.
He stood at Miss Temple's side; he was speaking low in her ear: I did not doubt he was making disclosures of my villainy; and I watched her eye with painful anxiety, expecting every moment to see its dark orb turn on me a glance of repugnance and contempt. I listened too; and as I happened to be seated quite at the top of the room, I caught most of what he said: its import relieved me from immediate apprehension."
Basically what is happening here is a man, Mr. Brocklehurst, is coming to where Jane is. Mr. B knows something that Jane did in the past and she is scared because he promised that he would tell what she did. This is bad because the people around here don't know her "villainy" and so they would shun her if they knew what she had done. Her mood in this is scared and meek.
This mood is contrasted by a very complex and educated diction and syntax. She uses a very extravagant diction throughout but when her character is called into question she starts to increase the complexity of her language. Whatever she did probably made her look like a street orphan and she didn't want to seem like that to the audience so she tries to appear educated. She uses words like villainy to describe what she did which makes it seem more sophisticated. A villain normally has a plan and therefore has some sort of thought and effort put into what they did. She is once again trying to make the bad things she did look more educated. She feels like the audience is looking down on her so she uses words they would likely not know to make them feel less than her. This is her defense mechanism.