Ok, I found the article about Susan. =) Here's an excerpt from it, I underlined what C.S. Lewis said about her.
Point Five is that just because Susan does not travel to Aslan’s country in The Last Battle does not mean she will never get there. Lewis makes this point himself in a letter written on January 22, 1957 where he states, “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 is plenty of time for her to mend, and perhaps she will get to Aslan’s country in the end—in her own way” (Letters to Children 67).
While time has ended in Narnia, it continues in our world. There are other characters left alive in England, and presumably any of them desiring to go to Aslan’s country after experiencing death on Earth will be allowed to do so. This list includes not only Susan but also Marjorie Preston, Mrs. Macready, the Telmarines who returned to Earth, the former bullies from Experiment House, and even Harold and Alberta Scrubb.
At the end of The Voyage of the Dawn Treader, when Lucy asks Aslan, “Will you tell us how to get into your country from our world?” he promises, “I shall be telling you all the time” (247). From this we may conclude that after the last chapter of The Last Battle, Aslan will continue to tell Susan and the other characters still in England the way they can reach his country.
Link to full article:
ClickyHope this helps! =)