Who is September from The Girl Who Circumnavigated Fairyland in a Ship of Her Own Making and what is their importance?

September is the novel's central character and protagonist, a twelve year old girl described as "ill-tempered and irascible", although she never really displays those characteristics over the course of the narrative, perhaps because she spends all but two or three pages of it away from the environment in which she WAS, perhaps, irascible and ill tempered. The characteristics she does display on her journey through Fairyland are determination (that sometimes verges on obstinacy), courage (that sometimes verges on foolhardiness), and compassion. This last is perhaps most important, in that it can be seen as a manifestation of at least two of the novel's main themes. The first is the power of choice (in that September's choices are often defined by her compassion for others). The second is self-sacrifice (in that September's choices are also often defined by her caring more about what others need than what she herself wants). September's physical, emotional, moral and spiritual journey through the narrative is, in many significant ways, modeled on the archetypal Hero's Journey, and as such is a manifestation and/or embodiment of the third of the narrative's primary themes. Ultimately she is, as the Marquess disparagingly calls her, a "good girl", described in narration as, at the beginning of her journey, being somewhat heartless in the way of all young children. But eventually, over the course of the narrative and after undertaking her Hero's Journey, she becomes a stronger, wiser, more worldly and more adult human being - which is, after all, the PURPOSE of such a journey.