Chaos and order
The primary theme of the novel has to do with chaos and order. Each of the sisters are tempered to better in one of those than the other; Ruthie prefers the chaotic world of Aunt Sylvie's cluttered home, but Lucille craves normalcy, order, and predictability. This dilemma first arises when their mother kills herself, leaving the girls in a state of absolute chaos.
Each daughter deals with this in their own way, but by the end of the novel, they have come to represent chaos and order. Ruthie's life is chaotic, introverted, and indulgent, whereas Lucille obeys convention, moving to Boston to find a job and a normal life. Both are lonely without each other.
Sisterhood
The challenge that faces the sisters is severe. Without their parents, without their grandmother, they are left in the custody of an under-qualified woman. Their relationship is stressed by their environment, by Aunt Sylvie's wild temperament, and ultimately, by their personalities. The question at the end of the novel is, "Will these sisters reunite, or have they separated permanently?"
Death and family
The family shuffles the girls around following the deaths of their matriarchs (the mother and grandmother are both dead). The novel deals with the girls' independent and communal attempts to make sense of life in light of death, specifically the traumatizing suicide of their mother.
The suicide of the mother indicates another issue: The prevalence of mental health issues in their family. Since the mother killed herself, her daughters are incredibly likely to develop serious depression, and by the end of the novel, both daughters are on the cusp of serious existential crises, Ruthie in her poor social development and isolation (she's becoming more like her Aunt Sylvie), and Lucille in her boring, lonely, normal life.
