Walsh may be best known as a member of the pop group Girls Aloud. Her film and television credits include This Is Personal, Dream Back, and Horrid Henry: The Movie.
The show, which is based on the story and characters from William Steig's book Shrek! as well as the DreamWorks Animation film Shrek, features book and lyrics by Pulitzer Prize-winner David Lindsay-Abaire, and music by Jeanine Tesori.
Walsh will join a company that also features Nigel Lindsay (Shrek), Nigel Harman (Lord Farquaad) and Richard Blackwood (Donkey).
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