Though it seems like our only encounter with Mother is in Chapter 1, her presence actually weaves the whole book together through letters and Moon Shadow and Windrider's thoughts of her. At the beginning of the book, Mother is the only link Moon Shadow has to his father and his kite-making. We can tell that Father has a tender place in Mother's heart because she is usually so hesitant to talk about him. Her actions speak more loudly: she's always lighting incense for Father and spiritually sending him her best wishes.
Importantly, Mother is one of the few examples we are given of a Tang woman, seeing as how we do not meet any in America because of various laws. Before you think Mother is way sentimental and a damsel in distress, remember that Mother is the one working the rice paddies, watching the chickens and the pig, taking care of her son and Grandmother, and taking care of business while her husband is thousands. We see an inkling of how the almost exclusive immigration of Chinese men to America changed the family and gender dynamic and meant that women were largely the ones running the show in China.
Mother is a constant figure of love and strength in Dragonwings. She lets Moon Shadow make up his own mind about going to America, even if it means she'll be without her partner and her child at home. She devotedly goes to the schoolteacher and has letters written to Windrider and Moon Shadow to maintain communication. One of the biggest moments is when she hears of Windrider's decision to pursue flight and specifically asks Moon Shadow to give him all the support that he needs, enough for her share since she is far away. Mother never knows about Windrider's dream of the Dragon King; she doesn't need to in order to have faith in Windrider and his passion.
Never one to doubt, Mother is a huge source of support for both Windrider and Moon Shadow throughout the story. Thinking of her might make the Lee men sad and nostalgic, but it also keeps them going in a way, giving them strength to be better people. We are made to believe that this faith and love pay off since Father is on his way to bring Mother to America at the book's end.