She is also the chairman of Artex Securities, and reportedly helped FLC chairman Trinh Van Quyet and his company manipulate stocks.
Quyet and the company’s accountant and his sister, Trinh Thi Minh Hue, were arrested earlier.
Quyet’s other sister, Trinh Thi Thuy Nga, deputy director at Artex Securities, and Nguyen Quynh Anh, its general director, were also arrested.
Dung, 44, was the chief lawyer at SMiC Law Firm established by Quyet and his associates. She later assumed senior management roles at FLC, including head of legal and project development department and general director.
She resigned as general director in March this year.
On Wednesday, Dung was also fined VND70 million ($3,000) for concurrently being a board member at seven companies. The Securities Law caps that at five.
The case that led to the investigation of Quyet and others began on the afternoon of January 10, when Quyet sold 74.8 million FLC shares, but the State Securities Commission of Vietnam (SSC) only received notice of the sale by the evening of that day though regulations require a notification three working days in advance.
On January 11, the Ho Chi Minh City Stock Exchange (HoSE) issued a notice cancelling the transaction, an unprecedented move in the Vietnamese stock market. Many investors have their investment refunded.
Quyet was fined VND1.5 billion ($65,800) by SCC on January 17, the highest level under current securities regulations, and his trading was suspended for five months.
It was the second time that Quyet was fined by the SSC for the same offense. In November 2017, he was fined VND65 million for selling 57 million FLC shares without proper notice.
Quyet began his career as a lawyer in 2001, when he and his associates established the SMiC Law Office, which later became the SMiC Law Firm. He also established a number of businesses and the FLC brand was formed in early 2010 after merging all of them.
FLC's charter capital stood at VND10.5 trillion (over $459 million) in early 2021, after more than 10 years of operation.
As of January 2022, the FLC chairman owned over 215 million FLC shares, equivalent to approximately 30 percent, as well as tens of millions of stocks in related companies like ROS.