Throughout the story, Jing-Mei and her mother engage in a battle of wills over her playing the piano. Once Jing-Mei completes her disastrous talent show performance, she assumes that she "would never have to play the piano again," but her mother treats her as if the fiasco had never happened. Jing-Mei argues that she isn't going to play the piano anymore, and she sees her mother's chest "heaving up and down in an angry way." She physically drags her on to the piano bench and declares that she will only accept an obedient daughter. When Jing-Mei says that she wishes she were dead like her mother's other babies from China, her mother is "stunned" and seems to blow away "like a small leaf."
Jing-Mei says that she spent the next several years disappointing her mother, "asserting [her] will, [her] right to fall short of expectations." She could have gotten better grades or gone to a better college. They never discussed the piano again; there were no more lessons. When her mother offers her the piano, she says what she's only told Jing-Mei before, that she has talent but that she just doesn't try. This, to me, sounds more like resignation: her mother isn't sad or angry, but, rather, she simply believes that her daughter could be more than she thinks, and she's given up trying to convince her daughter of that. The fact that Jing-Mei feels "proud" and "as if the piano were a shiny trophy that [she] had won back" seems to indicate that she thinks of the piano as proof that she has finally won this battle of wills. Her mother has given up, and perhaps she has learned to recognize that only Jing-Mei can convince herself that she is capable of more.