The ending symbology
The symbolism of the novel's ending is this: the mysterious effects of Maribel's injury are reversed upon her mother's decision to immigrate back to Mexico, as if to suggest that it were some kind of spiritually attachment to their homeland which would heal life's most pressing problems. Maribel's restrictions are symbols for those "pressing" problems, because the pressure of her injury makes her life radically different and also quite difficult in comparison to normal time. The reversal is a cyclical symbol for healing.
The suffering friend
The friend who is closest to Maribel in her suffering is the son of the Toro family, Mayor. He wants to be near to Maribel because something about her allures his sensitivity and his proclivity to be curious. He wants to know the valuable person that is usually overlooked. By loving Maribel, he experiences a private and secret reward in her friendship, and he also is given a chance to gain honor in the reader's opinion by defending Maribel against bullies. He experiences a lot of suffering because of his desire to support Maribel, making him a Christ-character.
Mayor's love
Mayor's love is a symbol for hope in the novel, because his character suggests a future of better times by inspiring Maribel and her family's imagination. His love is effective in causing changes in Maribel's life, but not to the intended effect. This makes the symbolism even more nuanced; because Maribel returns to Mexico leaving Mayor behind, the love between them becomes a symbol for hope that survives through seasons of disappointment and mourning. Their love is more symbolic than literal because of this, and therefore the symbol is stronger.
The bully
The bully is a symbol for the archetypal forces of evil. It is one thing to compete in a fair competition for honor or gain, but to use one's force to subdue an innocent and defenseless victim is a kind of domination that arouses in emotional readers a kind of hatred and bitterness. The bully's behavior is deeply triggering, emotionally, but that is a complicated problem because Alma must realize that whether she wants people to treat her daughter that way or not, the world is the way it is. The bully is a metaphorical reminder that life tends to add suffering to suffering. The powerful are more insulated by privilege, whereas the powerless are subject to myriad trials.
The death of the father
This is Chicano literature, and so the motif of the dying father is probably aligned with the genre to represent the slow death of the past, mourned deeply through heritage and cultural lifestyles. The death of the father is a sign of nature proving to the survivors of his death that the order of the past will end, and that means an introduction of chaos. The death has patriarchal overtones as well, because the father symbolizes the family's relationship to money. He worked in a system of economy and government that makes life very difficult for people at the bottom, so his death leaves room for considerations of fairness and life's inherent worth, et cetera.
