Chung Yoo-Ra is the equestrian daughter of Choi Soon-Sil, the close confidante of impeached ex-president Park Geun-Hye.
Chung Yoo-Ra is the equestrian daughter of Choi Soon-Sil, the close confidante of impeached ex-president Park Geun-Hye and the woman at the heart of the scandal which toppled Park.
Choi -- dubbed "the female Rasputin" for her strong influence over Park -- is on trial along with the ex-president.
Chung was arrested on a Korean Air flight from Amsterdam early Wednesday and was escorted off the plane at Incheon by a team of prosecutors to face a handful of journalists and television cameras.
Prosecutors say cash for Chung's equestrian training came from electronics giant Samsung, which had handed over the money as part of an attempt to curry favour with her powerful mother.
However, a Seoul court ordered her released Saturday.
"It is difficult to accept the reason and the need for her arrest", the Seoul Central District Court said, turning down the prosecution's request to formally arrest the 21-year-old.
The court noted basic evidence had already been secured by prosecutors and she was not an active part in the case.
Following the decision, Chung, who had been in custody since being extradited from Denmark Wednesday, said: "I'm truly sorry for having caused so much concern to many. ... I will sincerely reply in questioning by prosecutors."
She is accused of receiving bribes from Samsung, illegally moving money abroad and violating South Korean laws on the handling of foreign currency during her stay in Europe.
It is also alleged Chung received undue admission and grading favours from Seoul-based Ewha Woman's University.
Chung has said she had no knowledge of the "special treatment" she allegedly received, adding she knew nothing of what transpired between her mother and Park.
The disgraced former president was kicked out of office in March amid public disgust at the influence of money on South Korean politics.
Park and Choi are currently in jail and on trial for allegedly accepting or seeking millions of dollars in bribes from the country's huge conglomerates, including Samsung.
Samsung heir Lee Jae-Yong is being tried separately while Shin Dong-Bin -- the chairman of retail giant Lotte, the South's fifth-biggest conglomerate -- also stands accused.