What is the central theme in the full length novel? How does that theme convey itself through character, setting, and symbol? What are the examples of this theme as it appears throughout the novel?

The central theme can be expressed in a few different ways. One can be the resilience of the human spirit. In her book, Brooks particularly focuses on female courage.
This central theme is mainly conveyed through the character of Anna Frith. You may wish to discuss the events that describe how she manages to save her own child and Mrs. Bradford's illegitimate child.
The setting of the story definitely highlights Anna's courage in the face of adversity. Year of Wonders is set in the village of Eyam in Derbyshire, England, in the year 1666. History tells us that the Black Plague assaulted London society in the summer of 1665. More than 15% of the population died during that terrible summer. For more on the plague, please refer to the link below.
The dark, sinister setting of the story serves as the backdrop for many of Anna's courageous exploits. An example of this type of setting can be found in Part Two, Chapters Four and Five, which describe Anys' murder and the aftermath, when the villagers find themselves increasingly circumscribed by their ordeal.
An important symbol in the story are the herbs used by Mem and Anys Gowdie (and later Anna and Elinor Mompellion). In this novel, women wield the power of herbs to bring about comfort and healing to the stricken.
After the deaths of Mem and Anys Gowdie (the novel's female faith healers), Anna and Elinor are able to utilize the information from one of Avicenna's five-volume medical treatises to benefit their fellow villagers. For more on how Anna and Elinor utilize herbs like wolf's bane, please refer to this excellent link— Anna's Herbal: An Education In The Healing Power of Herbs. Also, in Part Two, Chapter Four, you may be interested in how Anys uses a special salve to bring Jamie temporary relief as he lays dying of the plague.
The novel's focus on how women are able to transcend affliction with courage is certainly supported by its reliance on important symbols, forbidding settings, and compelling characters.
https://www.historic-uk.com/HistoryUK/HistoryofEngland/The-Great-Plague/