As we mention in the "Narrator Point of View" section, the tone suggests that grown-up Waverly is looking back on her less-than-ideal childhood. To this end, she can get kind of cranky with her mom, taking little digs at her to show us what a pain she can be. But since Waverly-the-adult is in the mix, she also examines her own behavior with a pretty harsh eye, like when she points out "how wicked I was being" (11) when she asks her mom about Chinese torture.
As narrator, Waverly also tries to weigh the situation evenly instead of just judging her mother. So when she says, "My mother imparted her daily truths" (3), what starts as a sort of sarcastic jab morphs into a more compassionate understanding as Waverly explains her mother's desire to "help my older brothers and me rise above our circumstances" (3). Does Mom bug her? Yup—but as Waverly looks back, she tries to give her mom the benefit of the doubt, too.
That said, an atmosphere of general sadness pops up all over the text. Waverly doesn't ever come out and cry or tell us how unhappy she is; instead, she lets her descriptions tell us how she feels. For instance, when she describes her life after becoming a chess champion, she says:
I no longer played in the alley of Waverly Place. I never visited the playground where the pigeons and old men gathered. (51)
She never says she's sad, but in listing things she once enjoyed and doesn't get to do anymore, we can easily draw our own conclusions. A change like this would bum anybody out, and though she doesn't declare her feelings, Waverly makes sure we feel it.