Jing-mei says she feels like worms and toads are crawling across her chest because she feels bad about yelling at her mother.

Jing-mei has been trying desperately to please her daughter.  Her mother tells her that she needs to be a prodigy, to make her proud.  Jing-mei is unable to be successful though, and in an argument she tells her mother she does not want to play the piano any more.  This argument happens after the talent show, where Jing-mei embarrasses her mother and herself.  She is feeling frustrated and hurt.

You want me to be something that I'm not!" I sobbed. " I'll never be the kind of daughter you want me to be!"
"Only two kinds of daughters," she shouted in Chinese. "Those who are obedient and those who follow their own mind! Only one kind of daughter can live in this house. Obedient daughter!"

Jing-mei shouts that she wishes she were not her daughter, and regrets it when she says it.  She knows her words will hurt her mother, but she is hurt and frustrated herself.  She wants her mother to accept her for who she is, not push her to be someone she is not.