Who played the ADULT Lucy in Chronicles of Narnia: The Lion, the Witch, & The Wardrobe"?

Rachael Henley did. While Georgie Henley starred as Lucy Pevensie for most of The Chronicles of Narnia: The Lion, the Witch and the Wardrobe, for the shorter epilogue section set some fifteen years later, Rachael took over the role. As of 2007, this is Rachael Henley's only film performance.