The film is slated to debut next summer, on the 75th anniversary of the publishing of Mitchell's famous novel, "Gone with the Wind."
Rachel Frey, who owns the 1887 Trammell House off the Loop in downtown Marietta, said she didn't know what she was getting herself into when the producers called her up to ask about filming in her home.
"They used our house to film several scenes and (the producer) said, 'Would you be interested in playing Margaret Mitchell?' and I thought they were joking," said Frey, who has loved "Gone with the Wind" ever since she read it in the eighth grade.
"They said, 'All you have to do is sit at a desk and write.' I had no idea. I'm not an actress," Frey said.
The actors in the documentary portray scenes from Mitchell's life, while a voiceover describes the events.
Documentary producer Pamela Roberts of Atlanta said when she saw Frey, she knew she had to cast her as the celebrated Southern novelist.
"When we met her, she looked like the mature Margaret Mitchell. She's beautiful and Margaret Mitchell is beautiful, so she's our actress for Margaret Mitchell in the 30s and 40s," Roberts said.
This week, Roberts has been filming in the Whitlock Inn.
"Marietta has had the wonderful sense to preserve a lot of its fabulous buildings and history, and that is so rare in Atlanta," Roberts said. "You'd be surprised to find locations that match the timeframe that Margaret Mitchell lived in. Whitlock Inn was built in 1900. Margaret Mitchell was born in 1900. So when we discovered the Whitlock Inn and went inside and saw - this is the world that Margaret Mitchell knew."
Filming has also taken place at Oakton, the 1838 antebellum home of Michelle and Will Goodman, located about a mile from the Square, and at Larry Zenoni's house on Forest Avenue, a 1909 Craftsman bungalow.
"These people just opened their hearts and homes to us," Roberts said. "In this documentary, you're going to see these homes featured as part of the background of the reenactment."
Frey said it's fitting to be filming scenes from Mitchell's life in Marietta, because Mitchell had many friends here.
In July, Connie Sutherland, director of the Marietta Gone with the Wind Museum, and other city employees such as Joan Ellars and Shannon Barrett, decked out in gowns from Vintage by Judith, were filmed for a part of the documentary about Mitchell's mother, who was a suffragist.
"To study Margaret Mitchell is to learn about the history of the South. And the impact of the book, 'Gone with the Wind,' is really her ode to the suffering of the people in the South, and her great respect for what the women went through," Roberts said. "Margaret Mitchell was never an avowed feminist, but in her own way, if you look at the character of Scarlett O'Hara, I mean, she was a businesswoman. She was brassy, bold, she did what she had to do, and Margaret Mitchell really respected people like that because she was the same way. Margaret Mitchell says, 'Really what the book was about is gumption, people who had gumption and people who didn't,' and that really kind of sums up Margaret Mitchell. She had gumption."
Marietta is a popular destination for "Gone with the Wind" fans. Last year, as part of the 70th anniversary re-premiere of the film, Ann Rutherford, who starred as Scarlett O'Hara's little sister, visited the Square with other surviving cast members to share memories of acting in the sweeping Civil War romance that won 10 Academy Awards.
Thursday, the film crew shot a scene of Mitchell caring for her husband, John Marsh, after his heart attack.
"She got a 16 millimeter projector, which we had to go to great lengths to find one, and she showed him comedies, and she popped him popcorn, and she made him happy, and she did everything she could think of," Roberts said.
During the scene, the actors are filmed watching a movie starring W.C. Fields in a car chase, a scene meant to foreshadow how Mitchell herself was killed by a drunk driver in 1949.
"Everything that is in this documentary is from actual letters and writings from Margaret Mitchell, so that we are not telling stories out of school here. We're covering the bases of how she described her life through her letters," Roberts said.