The New York Daily News reported the 2-year-old mutt was scheduled to be destroyed in 48 hours when she got her chance at stardom.
She is to begin performances in the musical Oct. 3.
"The search for Sandy started last December and ended in March when we found Sunny," animal trainer William Berloni told the Daily News.
The newspaper said the show's director, James Lapine, selected Sunny based on her looks, temperament and other special skills, in particular her ability to walk on her hind legs.
"James said, 'I want the dog to dance,'" Berloni recalled.