I think that this is the central focus of the novel. The exact answer to this question is the novel, itself. Essentially, I think that Tan wants to make the argument that sexism is something that is applicable in both the East and the West. It looks different in both worlds, but it is there. It seeks to silence women and place them in gender stratified boxes. While the East's sexism is understood as "tradition," the West's is more insipid, more subterranean. For Tan, the critical defense mechanism that all of the women require to deal with such a structure is the advocacy of voice and the power to empower themselves through their voice. This looks different in both cultures. In China, the girls who became mothers later on were forces to actively resist a cultural setting that saw the violation of women's rights by men and even other women as something necessary. These girls in China had to summon the courage to raise their voice in protest. Perhaps, it was done through the channeling of other loved ones who perished, such as their mothers or other siblings. Yet, the raising of voice is what enabled these children who later become mothers to repel the sexist structure in China and assert their own voice.
In America, these women see their daughters "swallow their sorrow with Coca- Cola" and adopt Western ways. However, the sexist structure is still there. Tan makes the argument that these "modern" and "Western" girls still need their Chinese mothers to impart to them the lessons of the past in dealing with sexism. This is why each of the modern Chinese girls have to undergo two changes. The first is to repel the sexist structure, as their mothers did in China. The second is to not dismiss their mothers as being of the "old world." In each mother- daughter scenario, there is a reconciliation of sorts in which daughter must acknowledge that while mother's experience is of the old world, it is an applicable one because sexism exists. The coping mechanism thus for the daughters is to embrace the past in their mothers, embrace their identities as Chinese women, and fuse both into an advocacy of voice in opposing the Western brand of sexism that they find. It is here where Tan seems to be making an interesting argument that the mothers at least understood the experiences of the elders in battling sexism. This is something that the more cosmopolitan and younger generation has to undertake in order to fight the same demon in a different context.