On her third visit to Narnia, Lucy Pevensie shows a little more of her human side than she did during the adventures in The Lion, the Witch, and the Wardrobe and Prince Caspian. She is still in many ways the most perfect and sympathetic of the main characters in the book, as shown by her closeness to Aslan and her tendency to see him more than other people. However, when she accepts the request of the Duffers to explore the Magician's house to find a way to reverse their spell of invisibility, Queen Lucy displays both her heroic qualities and her flaws. She is courageous and compassionate – otherwise she never would have risked her own life to go into the study of an unknown magician and search for a remedy for people she hardly knows. However, as she reads the Magic Book, we discover her temptations and secret desires. She is jealous of her sister Susan's beauty and sorely tempted to use a spell to make herself "beautiful beyond the lot of mortals" (10.20). With a warning from Aslan, she resists this temptation, but then she gives in to insecurity and uses another spell to eavesdrop on a friend. As a result, the friendship is ruined forever.
Jealousy and insecurity aren't usually qualities we associate with Lucy, and we want to make it clear that, most of the time, she's the regular goody-two-shoes we got to know and love in The Lion, the Witch, and the Wardrobe. She still finds delight in the beauty of the natural world around her. She still loves all her companions, even her horrible cousin Eustace. And she still makes friends with strange old bachelors – her private meal with the Magician, Coriarkin, reminds us of her visit with Mr. Tumnus the Faun in the first Narnia chronicle. Lucy is definitely the narrator's favorite character (and, we suspect, the author's too). However, in this book, her character becomes a little more rounded as we realize that she has flaws which she needs Aslan's help to overcome.
At the end of the book, Aslan tells Lucy that she (along with her brother Edmund) will never be able to return to Narnia. Lucy is upset by this news, but we understand it: after her adventure on the Island of the Voices, there's really not much character development left for her.