Rosmah Mansor, the wife of former Malaysian prime minister Najib Razak, has been arrested by the country's anti-graft agency as part of an investigation into the 1MDB corruption scandal which helped bring down her husband.

The announcement came after she arrived at the Malaysian Anti-Corruption Commission (MACC) offices earlier to face a third round of questioning. She is to appear in court Thursday morning.

The MACC said it had arrested Rosmah ‘on investigations into money laundering after the MACC obtained permission from the Attorney-General's Chambers.’  Clad in a traditional lime-green outfit with a matching scarf, the 66-year-old appeared calm and was smiling as she made her way through a media scrum into the building.

The first time she was questioned on June 5 was for her alleged involvement in the transfer of 42 million ringgit (10 million dollars) into her husband's bank account from SRC International, formerly a subsidiary of 1MDB, a huge state development fund.

Her second interrogation lasted 13 hours. She is expected this time to stay in the MACC overnight until her Thursday court appearance.

Ex-premier Najib, who has denied any wrongdoing, is accused by US prosecutors of misappropriating some 4.5 billion dollars from the 1MDB fund, including nearly 628 million dollars that were allegedly transferred directly into his personal bank account.

Authorities in May raided several properties belonging to the couple, confiscating 284 Birkin handbags and 72 suitcases filled with cash and other valuables.

 Malaysians have since compared Rosmah to former Philippine first lady Imelda Marcos, who was notorious for her collection of designer shoes. Rosmah's expensive beauty routine - including 300-dollar haircuts, alleged facelifts and botox treatments - are still the subject of much national gossip.

Rosmah's lawyers, however, have disputed a claim that she spent 27 million dollars on a rare pink diamond.

Mahathir Mohamad, the country's new prime minister, reopened the corruption case against her husband after he defeated Najib in elections in May.

At least six governments - including those of the United States, Switzerland, Indonesia, Malaysia, Singapore and Hong Kong - have opened investigations related to 1MDB.

Earlier on Wednesday, Najib was questioned by the commercial crime unit over his involvement in 1MDB. Najib did not address the media after the session, as he made his way out from the back entrance of the building.

Both Najib and Rosmah have been barred from leaving Malaysia while investigations continue.

Najib has 32 charges against him, including abuse of power and criminal breach of trust.

He has been arrested twice, once in July and once on September 20, but was released on bail both times.

Najib's trial is due to start early next year.

US Attorney General Jeff Sessions has called the 1MDB scandal an example of ‘kleptocracy at its worst.’