Koenig, 31, is now a key member of France's jihadist movement fighting in Syria where she is involved in recruiting and spreading propaganda.
"She is an important member of the jihadist community, she is very active on social media. We know her very well," a high-ranking French anti-terrorism official told AFP.
Koenig, who had already appeared on a UN watchlist in September 2014, was added to the US State Department's list for encouraging sympathisers in France to attack French government institutions.
Her assets have been frozen in France since 2012, when she left for Syria to join her husband who was already fighting alongside IS, making her one of the first of hundreds of French citizens to join the group.
She was born in 1984 in the port town of Lorient in northwestern France, the youngest in a family of four.
She had an outwardly normal life until she met her first husband.
Fight over full-face veils
It was while married to the man of Algerian origin, who had been imprisoned on drug charges, that she converted to Islam, learned Arabic and began to call herself Samra.
She began wearing the full-face niqab veil and came into contact with Forsane Alizza, a local Islamist group also called the "knights of pride" which gained attention for its protests against France's 2010 decision to ban full-face veils in public.
Several former members of the group have since been linked to jihadist acts, such as Yassin Salhi who in June beheaded his boss and displayed the
severed head on the fence of a gas plant, surrounded by Islamic flags.
In 2010, while wearing the niqab, Koenig was discovered handing out leaflets calling for jihad near a mosque in Lorient. She was also often seen at the forefront of protests in Paris, fully veiled.
In 2012, when summoned to court for her actions, she refused to remove her veil, prompting an altercation with a security guard that she filmed and posted on YouTube.
After Forsane Alizza was disbanded in 2012 by the government, which called it a "private militia", Koenig opened several Facebook accounts calling for a holy war.
It was around the same time that she left the country for Syria.
In France, Koenig has come under scrutiny as part of a probe into the recruitment of a dozen youths from the southern city of Nimes who left to fight with Isis.
Like many other women who have left to join the militants, she is not allowed to fight, but often appears in propaganda videos.
In one of them, posted in 2013, she appears training with a shotgun in Syria.
In another she addressed propaganda messages to her two sons who still live in France with their grandmother.
"Don't forget that you are Muslim," she told the boys. "Jihad will not end as long as there are enemies to vanquish."
According to the UN watchlist, she often calls contacts in France from Syria, encouraging them to commit violent actions against designated targets such as French institutions or the wives of French soldiers.
A source close to the case, speaking on condition of anonymity, described Koenig as "highly strung" and said she had declared herself willing to carry
out a suicide attack.
However he said "these people often tend towards theatrics."
Koenig was one of three French nationals named on the list of 35 people from a variety of countries who were hit with sanctions or terror designations for their affiliation with the Islamic State group.
Maxime Hauchard, who has appeared in grisly Isis execution videos, and Peter Cherif, a member of Al-Qaeda's Yemen affiliate AQAP, were also named.
However it was the number of women on the list that was striking as Isis increasingly targets young Western women who play key roles in recruiting jihadists.
Scottish jihadist Aqsa Mahmood, who reportedly travelled to Syria last year to marry an IS fighter and who runs an English-language blog seen as a source of Isis propaganda, was also on the US list.
So was former British punk singer Sally Jones, who has worked to recruit other women to IS.