For nine months she has led the international mission to destroy Damascus's declared chemical agents, braving mortar fire, jetting between the Middle East, Europe and New York, and liaising with Moscow, Washington and maritime fleets.
Syria may have missed deadlines but with 93 percent of its declared chemical arsenal out of the country, Kaag is responsible for the only glimmer of good news to emerge from the horror of a war that has killed more than 160,000.
Her star is in the ascendancy at UN headquarters, abuzz with praise for the woman who at UNICEF worked with Jordan's Queen Rania and once dreamed of becoming a singer.
- 'Never stops working' -
The 52-year-old Kaag speaks fluent Arabic and diplomats say she has done an excellent job. She is respected too in Damascus, where some have dubbed her the "Iron Lady."
"She never stops working and practically never sleeps," one of her local employees confided to AFP.
What seems certain is another big job after her mission concludes in the coming months.
The media has touted her a possible successor to Lakhdar Brahimi as mediator on the stalled Syrian peace process although others tip her for a different post in the region.
She quashes any suggestion that a Western woman should find it difficult in the Arab world, saying she has always been treated with respect and never in a derogatory way.
"I think in many negotiations women have great assets," she told AFP in an interview, dressed in a black trouser suit, red top and high heels.
"You can bring different component parts -- be as strong and on message and negotiate, but I think we have a wider skill set available."
Her husband is a Palestinian former diplomat and having children who are half Arab can also be an asset, she said.
"You're one foot in, one foot out. But I think ultimately people judge you on the basis of what you bring, if you're sincere, if you're committed and if you're up to the task," she added.
- 'Keep your calm' -
As head of the joint UN-Organisation for the Prohibition of Chemical Weapons mission, she manages a staff of 110.
In Damascus she said mortars have fallen around the hotel where they live and work, and that she sent away some staff who were unable to cope.
"The fact that you don't get hit, you feel blessed but you know that you're in an active war zone."
It has been a stratospheric rise for the daughter of a music professor who moved to Egypt to study at the American University in Cairo as an undergraduate.
She has a masters degree from Oxford and worked in the private sector for oil giant Shell in London for two years before joining the Dutch foreign ministry.
Kaag decided to quit the job after meeting her husband in Jerusalem, signing up instead to the UN Relief and Works Agency which looks after the plight of Palestinian refugees.
In the last 20 years, she has lived in Jerusalem, Jordan, New York, Sudan and Switzerland, adopting one child and giving birth to three more, juggling marriage with a career.
She was previously number three in the UN Development Programme and UNICEF director in the Middle East and North Africa, during which she met Syria's first lady Asma Assad.
In her current job she has hardly taken a break. Her mother died since she moved to Damascus and she admits it is "very difficult" to see her children, aged 11 to 19.
Home is currently in east Jerusalem, where the family moved last year. Do they worry about her living in a war zone?
"They've been very impressed by my close protection, that gave them an immediate sense of safety," she smiled.
"They cope but they know it's finite and I've underlined that."
She describes herself as "results oriented" and with nerves of steel.
"I don't panic easily," she said. The rare exception being during a near crash on a tiny charter plane years ago.
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