 Strallen played the title role in the West End production of "Mary Poppins" opposite Gavin Lee as Bert, at the Prince Edward Theatre from 2005 (as a replacement to original cast member Laura Michelle Kelly) to 2006, when she left to join The Royal Shakespeare Company's musical production of "The Merry Wives of Windsor" in Stratford.She returned to "Poppins" in 2007, replacing Lisa O'Hare, and stayed with the production until it closed in January 2008.For her performance as Mary Poppins, Strallen was nominated for the Best Takeover Role Award at the 2006 Theatregoers' Choice Awards.