The close reader of the Chronicles should probably be aware of Susan's flaw of character long before (s)he reads Peter's account of it in The Last Battle. In dealing specifically with Books 1 and 2 in the series (all mention of book numbers is according to Lewis's authorship of the series, not the chronology of the series), the reader will notice a pattern that belies the true heart of Queen Susan the Gentle. While there are relatively few references to the fact in The Lion, the Witch, and the Wardrobe, they abound in Prince Caspian.
Susan's association with Peter, Edmund, and Lucy is her saving grace in these first books. It is in book 3 that we learn that Susan has been separated from her siblings by her mother while on a trip to the United States. Peter has remained in England with Digory (Professor) Kirk to study for an exam. The younger two are with Harlod and Alberta Scrubb and cousin, Eustace (hence the story for Voyage of the "Dawn Treader"). It is during this time that Susan changes and is "no longer a friend of Narnia."
It is Jill who informs the reader (in Last Battle) of Susan's distraction from Narnia. She points out that "she's interested in nothing now-a-days except nylons and lipstick and invitations. She's always a jolly sight too keen on being grown up (pg.135)." Based on this and other comments made about Susan, we can only assume that her problem is what the Bible calls "worldly lusts" (Titus 2:12). (which is in and of itself a statement on the status of the United States. Would Susan have been preserved without Western influence...?)
Why does Susan spend so many years in Narnia only to betray her beloved Aslan and commend the experience to flights of childish fantasy? The question is perhaps without answer; however there is evidence to support the idea that Susan's heart was never truly in Narnia. She did live the experience with her siblings, but coexistence does not indicate complete agreement. Three incidents in Lion indicate that Susan was more interested in being "grown-up" than being in Narnia.
When the children first arrive at the home of Digory Kirk, they assemble in the girls' bedroom to talk. During the course of the discussion, Susan remarks about the professor, "I think he's an old dear." It is Edmund who decides that she is being too matronly and retorts, "Don't go on talking like that." Only after Susan suggests that Edmund should perhaps go to bed does he accuse her of "trying to talk like Mother."
Incident two occurs when all four children have entered Narnia and have come to the home of Tumnus the Faun. Upon seeing the destruction of Tumnus's cave, it is Susan who first suggests that they return home and she wishes they "had never come." (Susan makes a similarly defeatist comment during the hunting of the White Stag on page 184.)
Incident three, though brief, is significant. Recall that it is Susan who questions the Emperor's magic. "Isn't there something you can work against it?" Her plea is met with a quick rebuke from Aslan.
Prince Caspian is loaded with evidence that Susan is playing the part of the motherly sister. I shall not go into all of the evidence (there is too much to include), however, there are a few worth mentioning. On page 122, Lucy sees Aslan and informs the others of His presence. Susan asks where Lucy thought she saw Him (a rather condescending question at best). Susan later decides to go against what Lucy says is Aslan's will by going downhill rather than up. On page 142, Susan says that Lucy is being "downright naughty" for wanting to follow Aslan. Recall that Aslan became visible only when the faith of the individual child allowed Him to be seen. Susan and Trumpkin are last to see Him. Finally, when forced to confront Aslan on page 148, Susan is speechless (a typical guilt response) and little revived by Aslan's forgiveness.
Sad though it may be, Susan's fate is all too predictable. She remains in Narnia and rules with her brothers and sister. She does not leave their counsel; why should she when the very nature of her position feeds the desire for which she has been inwardly longing. Having left Narnia at the end of Lion she responds by trying to resurrect a Narnian adulthood on this side of the wardrobe, a task impossible to accomplish. Returning to Narnia simply adds to her struggle by returning her to the place of her fantasy life without the former elements of that existence (which explains her more numerous accounts of rebellious acts in Prince Caspian).
Susan apparently represents the Narnian concept of the Biblical traitor. Her faithful facade is corrupted by faithless words and deeds. One would be reminded of Judas, who also betrayed his Lord despite his attempts to appear righteous. Sadly, Aslan had to have one of his flock fall away. Susan responded to this necessity by virtue of her inward desires.
