This is really the biggest turning point in the chapter (and quite possibly in Jing-Mei's life as well). Essentially Jing-Mei has transitioned into what she sees as free will and free thought (rebelling against her mother).
"So maybe I never really gave myself a fair chance. I did pick up the basics pretty easily, and I might have become a good pianist at that young age. But I was so determined not to try, not to be anybody different that I learned to play only the most ear-splitting preludes, the most discordant hymns" (138).
Jing-Mei, just like the child in the parable of the twenty six malignant gates, gets so caught up in not doing what her mother wants that she loses sight of everything else and ends up hurting herself.
"When my turn came, I was very confident. I remember my childish excitement. It was as if I knew, without a doubt, that the prodigy side of me really did exist" (139).
Like the other Joy Luck daughters, Jing-Mei takes her rebellion to the extreme as if to convince everyone (including herself) that she doesn't care what her mother says but just makes it clearer that she's only doing it because her mother has gotten to her.
"My mother believed you could be anything you wanted to be in America. You could open a restaurant. You could work for the government and get a good retirement. You could buy a house with almost no money down. You could become rich. You could become instantly famous. ...America was where all my mother's hopes lay" (132).
This is the classic American dream that we've been talking about throughout the book, but this is really the first time that it's directly mentioned by one of the characters. In terms of the story, this mentality is what sets off Suyuan's need for her daughter to be a prodigy of something (it didn't really matter what).
"And after seeing my mother's disappointed face once again, something inside of me began to die. I hated the tests, the raised hopes and failed expectations. Before going to bed that night, I looked in the mirror above the bathroom sink and when I saw only my face staring back–and that it would always be this ordinary face–I began to cry. Such a sad, ugly girl! I made high-pitched noises like a crazed animal, trying to scratch out the face in the mirror" (134).
This just shows the intense psychological effect that Jing-Mei's mother has on her. It is almost disturbing. The other joy luck daughters are affected similarly by their mothers' expectations and general parenting. Lena, for example, is so messed up as a child from of what her mother tells her that she continually imagines gruesome new ways that she might be killed or kill someone else.