Mary Lou Retton, who captured the attention of the nation when she won the all-around women's gymnastics competition at the 1984 Summer Olympics, had a "scary setback" as she fights a "very rare form" of pneumonia.

In the first update in four days, Shayla Kelley Schrepfer, Retton's daughter, related that things seemed like they were headed "on the up and up," but things took a turn for the worse on Tuesday.

"Basically at the beginning of this week, we were going on the up and up," Schrepfer said in the Instagram post. "We were so excited seeing so much progress. And then yesterday, we had a pretty scary setback."

Mary Lou Retton atop the podium at the 1984 Olympic games

From left: Ecaterina Szabo, Mary Lou Retton and Simona Pauca are seen during the women's gymnastics medal ceremony during the 1984 Summer Olympics at Pauley Pavilion in Los Angeles on Aug. 1, 1984. (Disney General Entertainment Content via Getty Images)

Mary Lou Retton looks on during a competition

Mary Lou Retton, former Olympic gold medalist in women's gymnastics, looks on during the 2009 Tyson American Cup at the Sears Centre in Hoffman Estates, Illinois, on Feb. 21, 2009. (Jonathan Daniel/Getty Images)

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Schrepfer did not say what exactly happened to cause the setback, but did say that Retton had a "better day" on Wednesday and that she was "just really, really exhausted."

"She is still in ICU. And we're just working through some things as far as her setback goes. So I just wanted to give an update there," Schrepfer said. "She had a better day today, which is great. She is just really, really exhausted."

Mary Lou Retton

Gymnast Mary Lou Retton of the United States, far right, waves to fans with her teammates during the 1984 Summer Olympics at Pauley Pavilion in Los Angeles. (Focus on Sport/Getty Images)

Schrepfer on Oct. 10 revealed that her mother has been in an ICU "over a week" with a "very rare form" of pneumonia. Since then, financial support has poured in as Retton "continues to fight." 

As of Thursday morning, a fundraiser page for the legendary Olympian had received more than $452,000 in donations. The crowdfunding campaign to help with Retton's medical bills initially had a goal of $50,000.

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The Spotfund page also noted that Retton does not have health insurance.

"GET WELL MARY LOU!! You are America’s Sweet Heart, and we are all rooting for you!" one donor wrote on the fundraising page.  

Retton is receiving treatment at a Texas hospital, according to The Associated Press.

Mary Lou Retton poses for a portrait

Mary Lou Retton poses for a portrait session for the 1984 Summer Olympics. (USA TODAY Sports)

Retton's win at the 1984 Olympic Games in Los Angeles marked the first time an American woman won the all-around gold medal or any individual Olympic medal in gymnastics.

She appeared in several films and television shows in the 1980s and 1990s and was inducted into the International Gymnastics Hall of Fame in 1997.

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After she retired from gymnastics, Retton became a motivational speaker and frequently shared messages about the benefits of proper nutrition and exercise. She also served on the President’s Council on Physical Fitness and Sports under former President George W. Bush.

Fox News' Chantz Martin contributed to this report.