According to the US Embassy and Consulate in SA, Brown assumed her role in January 2025.
US President Donald Trump's new administration is yet to appoint an ambassador to replace Reuben Brigety, who resigned in January in accordance with standard procedure during a change of a presidential administration.
The resignation takes place amid serious tensions between Pretoria and Washington, allegedly over South Africa's policies.
In his resignation notice in November last year, Brigety said: "US ambassadors serve at the pleasure of the President, and with the recent election in the US, the American people have expressed their choice for the future direction of our country, reflecting our shared commitment to democratic principles."
The relationship between SA and the US started to show cracks under Brigety after he accused the government of arming Russia in the ongoing war in Ukraine. This was after the docking of the Lady R in Simons Town Naval Base in December 2022.
An investigation into the matter found that there was no evidence to substantiate the claim that Lady R transported weapons from South Africa to Russia
News24 understands that Brown, who is expected to leave South Africa in March, will be replaced by David Greene.
A US Embassy official told News24 that Brown was retiring from the US Foreign Service, and would be returning to America after a "notable career in the international diplomacy".
"For 27 years chargé d'affaires Brown has served with dedication to strenghten U.S relationshps and partnerships around the world; the USmission to South Africa has thrived under her leadership," said the official.
Greene is expected to arrive in South Africa on 14 March. The US Embassy official said he would ensure continuity in leadership and the advancement of US priorities.
READ | 'They are sowing divisions': Ramaphosa slams AfriForum and Solidarity's Washington visit
According to information on the US Embassy and Consulate in Nigeria, Greene - a member of the Senior Foreign Service - joined the embassy in Abuja, Nigeria, as a chief of mission in August 2022.
Before that, he served as a deputy chief of mission and chargé d'affaires in Morocco from 2019 until 2022.
Previously, he served as a political counselor in Rabat from 2012 until 2015.
He has also worked in countries including Pakistan, Jordan, Egypt, and Vietnam.
Greene holds a bachelor's degree in government from Harvard University, a master's from the Fletcher School of Law and Diplomacy, and a master's from the US National War College.
His appointment comes a week after Brown represented the US at the first foreign ministers meeting held under South Africa's G20 Presidency.
The meeting continued despite the absence of US Secretary of State Marco Rubio and Treasury Secretary Scotty Bessent, who skipped the meetings amid a diplomatic fallout between Pretoria and Washington.
The tensions between Pretoria and Washington are at an all-time low, with diplomacy tactics out of the window as Trump signed his latest executive order cutting all funding to South Africa and announcing refugee status for Afrikaner farmers.
During his State of the Nation Address two weeks ago, President Cyril Ramaphosa asserted the government's position on Trump's latest move against South Africa.
READ | 'They are sowing divisions': Ramaphosa slams AfriForum and Solidarity's Washington visit
In the latest development, Afrikaner lobby groups AfriForum and the Solidarity Movement have traveled to the White House to deliver a "Washington memorandum", and have asked that the US provide humanitarian assistance for Afrikaner development.
This after Trump issued an executive order to freeze funding to South Africa because his view was that "terrible things" were happening in the country.
Trump signed the executive order earlier this month and offered to resettle Afrikaner victims of "racial discrimination".
While the groups welcomed the political pressure Trump put on the SA government, they rejected the withdrawal of aid and the classification of Afrikaners as refugees.
On Thursday, Ramaphosa accused the groups of sowing divisions in the nation. AfriForum CEO Kallie Kriel rejected this.