In The Last Battle, Susan was the only Pevensie that survived the train wreck on Earth which sent the other children to Narnia after the Last Battle. Susan choses not to return to Narnia. Peter says that she is "no longer a friend of Narnia", and (in Jill Pole's words) "she's interested in nothing now-a-days except nylons and lipstick and invitations." Eustace Scrubb says that she said, "What wonderful memories you have! Fancy you still thinking about all those funny games we used to play when we were children," and Polly Plummer adds, "She wasted all her school time wanting to be the age she is now, and she'll waste all the rest of her life trying to stay that age. Her whole idea is to race on to the silliest time of one's life as quick as she can and then stop there as long as she can." So, Susan does not enter the real Narnia with the others at the end of the series. It is left unknown whether or not Susan's absence is permanent, especially since Lewis said elsewhere that "The books don't tell us what happened to Susan. She is left alive in this world at the end, having by then turned into a rather silly, conceited young woman. But there's plenty of time for her to mend and perhaps she will get to Aslan's country in the end...in her own way." In his Companion to Narnia, Paul F. Ford writes at the end of the entry for "Susan Pevensie": "Susan's is one of the most important Unfinished Tales of The Chronicles of Narnia", but adds in Footnote 1 for that entry: "This is not to say, as some critics have maintained, that she is lost forever ... It is a mistake to think that Susan was killed in the railway accident at the end of The Last Battle and that she has forever fallen from grace. It is to be assumed, that as a woman of twenty-one who has just lost her entire family in a terrible crash, she will have much to work through; in the process, she might change to become truly the gentle person she has the potential for being."
I wonder if the film makers will keep her in 'The Last Battle'(assuming they make it)since they have put so much effort into showing that Susan is a clever person. What do you think? I like to believe that she eventually turns to faith and excepts Aslan again.