During 2007–08, Kelly played the role of Galadriel in the original London production of The Lord of the Rings – The Musical at Theatre Royal, Drury Lane. The show began previews on 9 May 2007, with an official opening night of 19 June 2007. Kelly played her final performance on 2 February 2008, and was replaced by Abbie Osman.
A new single, "What's It All For?" (written by singer Judie Tzuke) was released as a digital download on 5 March 2007. It was followed by the release of her album, also titled What's It All For?, with the three new tracks and a selection of others from The Storm Inside, which was released in 2006.
Kelly made her feature film debut in 2007 as Lucy Barker in the Tim Burton/DreamWorks film Sweeney Todd.