The musical will premiere at the Ahmanson Theater in Los Angeles after Oct. 2, the Los Angeles Times reported.
Actor and comedian Steve Martin played a bunco itinerant preacher in the move, and Shields' role in the play is as Mara, the small-town girl who doesn't buy his line.
"That's the nature of a new musical, the time it takes from an initial idea to its realization," Tony-winning director and choreographer Rob Ashford told the newspaper.
The storyline in the play is modified, the report said, and Marva is now a widowed single mother, and "the heart of" the drought-stricken Kansas town where Jonas, the preacher, pitches his tent.
As an actress and singer, Shields has appeared in plays, but this is the first time she has put so much time in creating a character, she said. And, she said, it is the first time she's been asked to sing in her own voice.
"I'm used to singing in a character voice, being told, 'Do it with an accent, or do it in a '40s style,' and with a wig, or a dialect. When they say, 'We want to hear you,' I think, 'What do you mean? I imitate people, that's what I do,'" Shields said. "You feel naked."