Good question! When thinking about the mood of a short story we can also consider the content of the story to help us determine what mood is adopted. This short story, like "Two Kinds", features the conflict between a Chinese mother who has immigrated to the States and her daughter, born in the States, who wants to forge an individual identity for herself. The mood can thus be said to capture the increasing resentment of Waverley against her mother for her insistence of showing her off but also her increasing defiance and stubbornness in her desire to be her own person. To me, a key passage is at the end of the story, when Waverley imagines a chess game to explore the conflict between herself and her mother:
In my head, I saw a chessboard with sixty-four black and white squares. Opposite me was my opponent, two angry black slits. She wore a triumphant smile. "Strongest wind cannot be seen," she said.
This imagery and the mood employed shows the reader how Waverley feels and views her mother's intrusion - she is depicted as a dangerous, frightening figure with "two angry black slits". The very last line of the story, "I closed my eyes and pondered my next move", seems to capture the defiance expressed by Waverley throughout as she considers what her next move in this "game" will be to beat her opponent (her mother) and achieve independence.
You may want to consider reading the book from which this short story is taken - The Joy Luck Club, which is an excellent book developing the conflicts between four sets of Chinese mothers and daughters.