At 8.46am, when on any other week day Jenner would have been in her 105th-floor office at the top of the centre's North Tower, a plane smashed into her building between the 93rd and 99th floors, causing it to explode in a fireball.
As panicked people ran towards her screaming "fire, fire", Jenner thought a bomb had gone off. She started to run and didn't stop until she was well clear of the building.
Outside she saw flames coming from the tower and then suddenly the street went quiet.
Ten years later, on holiday in Spain from her London base, Jenner can recall the exact sequence of events in chilling detail.
"It's like one of those bizarrely vivid recollections, it was very, very quiet on the streets. People were disappearing. I saw the glass and paper falling before I suddenly realised it was dangerous and I had to get away."
At 9.03am a second plane hit the South Tower. Thirty-four minutes later another one crashed into the Pentagon. Twenty-five minutes more, at 10.03am, United Airlines Flight 93 crashed into a field in Pennsylvania. A New Zealander, Alan Beaven, was among those who died on that flight after passengers attacked the terrorists in the cockpit.
America was under attack in a meticulously planned al Qaeda terrorist operation just as President George Bush was reading a book to pupils at the Emma E. Booker Elementary School in Sarasota, Florida.
The President went on to launch a global war on terror, to declare the conflict a struggle between "good and evil" and to say "either you are with us or you are with the terrorists".
Almost 10 years later, this May, hundreds of people cheered outside the White House when Bush's successor, Barack Obama, announced the capture and death of al Qaeda leader Osama bin Laden.
Nearly 3000 victims - including firefighters, paramedics and police - and 19 hijackers died in the terror attacks that September morning.
It took just one hour and 42 minutes for both towers to weaken, buckle and collapse after the two jets, loaded with fuel, set off an inferno from which there was no escape. As firefighters desperately tried to reach people high in the building using the stairwells, some of those trapped leaped to their deaths rather than face burning alive.
No one on the floors above both points of impact survived. Jenner says it wasn't until the second plane struck that people really started to think something catastrophic was happening.
"As a New Zealander I didn't really understand fear, but that was the moment when the world changed for me.
"That day I was fearful for my life, I wondered how on earth I could be caught up in it. It was just chaos, unreal, I couldn't comprehend it.
"I was in that flight-or-fight mode, quite bewildered. I saw a lot of fire trucks pulling up, and police and fire officers going in. I found that phenomenally brave. I just wanted to get as far away as possible."
Eventually, she managed to get a cab to her home on the Upper East Side but she wasn't there for long. In the afternoon she made her way to her boss' apartment where they began the enormous task of trying to account for their colleagues.
Meanwhile, around the world people sat staring at their televisions, transfixed by the sight of the burning World Trade Center and watching over and over the image of a plane flying into a New York high-rise framed against clear, blue sky. And then a second one.
At a Fiji resort, Aucklander Ralph Beaven was having brunch with his family when he noticed other guests crowding around a TV screen.
He assumed an engrossing sports game was capturing their attention until he wandered over to have a look. Beaven, too, was transfixed but at that stage he was not alarmed. Alan, his younger brother, was in America but in another city.
Later that day Beaven's sister rang him from Florida. That morning Alan had boarded a flight bound for San Francisco, where the 48-year-old environmental lawyer was about to try a case.
It was United Airlines Flight 93 and it left Newark International Airport in New Jersey at 8.42am with 37 passengers and seven crew aboard.
At 10.03am it crashed into a field 129km south of Pittsburgh. Passengers, realising they had been hijacked, rang their loved ones. Some wrestled with their captors, succeeding in diverting the plane from its target, believed to be the US Capitol or the White House. No one survived.
Alan was one of two New Zealanders who lost their lives on September 11. The other was John Lozowsky, who held dual American-New Zealand citizenship. He had been working in New York as an IT consultant, but had lived in New Zealand for 10 years before moving to New York in 1999.
For a long time after the crash, Ralph Beaven was angry with his brother. He blamed him for being on the doomed flight, wanting to know of all the connections he might have caught, why the one he chose was United Airlines 93.
"It is amazing that he was on that flight at that time - those are horrendous odds."
The odds were also stacked against Jenner's employer Cantor Fitzgerald. Its offices ranged over the North Tower's top five floors and out of almost 1000 staff, 658 were at work that day.
Jenner says at first the people gathered at her boss' apartment thought most of their colleagues would have got out.
"We thought we were just figuring out where people were, making a list."
By the evening of September 12, they began to realise what they were dealing with. The list of safe people was too short and made up entirely of staff who hadn't been in their office at the time.
The company lost the most employees of any World Trade Center tenants, and considerably more than the New York police and fire departments.
In the days that followed, working on little sleep, Jenner and her surviving workmates split into two groups.
One group worked to re-establish the crucial bonds trading market, the other - and the one Jenner was involved with - worked with families of missing employees.
"It was long hours, horrible hours, we were suddenly in a war zone, dealing with people, trying to help them; some were very angry.
For a lot of people like me, you just work through it. If you can resume some sense of purpose, at least in the initial stages it helps. It wasn't until a lot later that I felt the shock of it all.
"But that's one thing that people don't appreciate. It wasn't just one day, it went on and on for days, weeks."
She suffered nightmares of falling and of fire that became increasingly difficult to deal with, and then in December, she says, it was like a light switched on for her.
"I thought to myself, all my friends and family are still alive and missed me. It was time to be with them."
So she came home.
"I remember being on the plane and I couldn't believe I'd stayed. It felt like it had been a very long time. It was only a few months but it felt like a year.
"In New Zealand it was peaceful and it was nice to feel that."
She was not alone. Other Kiwis in New York also came home.
On September 11, computer programmer Richard Dann was at the same subway station as Jenner when the first plane hit. He too ran, and recalls turning back to look just as the second plane ploughed into the South Tower. He saw a huge ball of flame and people leaping to their deaths and the towers collapsing.
He, his wife and young baby were back in New Zealand permanently by December, about six months ahead of schedule.
"Everything became more stressful. It was difficult to get around, there were anthrax scares, threats on the subway, queues everywhere. It was better to be out of it."
Karla Hale came home too, not straight away but eventually.
"New York changed for me," says the Mt Maunganui acupuncturist.
"I still love it but after going through something like that, it's always in the back of your mind that it could happen again."
For Hale, 9/11 shaped what she has done with her life, and how she has done it.
"Thousands of people went to work and didn't come home. Now, if I decide I'm going to do something I just do it. I take more action on my decisions."
For Dann the lasting impact is more in his memory than the shape of his life since.
"I was there, and I remember it but it's not a major influence on my life," he says.
Jenner also insists that what she experienced is no different from any other trauma people go through.
It did, however, take her a long time to feel safe at work again.
"It has affected my perspective on my work. I think I have a higher degree of emotional attachment to my work, I'm more aware of the people I work with. In normal working life most people don't experience that but I think it is something the people who were in the CTV building in Christchurch in February would relate to."
For Ralph Beaven time has helped heal the emotional scars and while he won't call it closure, the death this year of Osama bin Laden was a significant step.
"I was particularly pleased they captured him. I am full of admiration for the way America has committed to anti-terrorism throughout the world."
Beaven says he doesn't mull over what his brother might have gone through on that flight.
Three years ago he met United flight attendant Judy Jackson, who was in New Zealand for six months with her doctor husband while he worked at Southland Hospital. Jackson was compiling information on crash victims for a memorial that will be built at the site next month.
There is some evidence - although Beaven prefers to call it conjecture - that Alan was one of the passengers on United 93 who tried to storm the cockpit and confront the hijackers.
"But there was never any official report. I don't really think about that at all. I don't feel a need to know, it wouldn't help me."
Beaven has lost touch with his niece and nephews and with Alan's second wife, Kimi, since the crash. But he is planning a trip to the US, to the 9/11 memorial.
"Not this year, but at some stage. I would like to get there but it's not something I relish doing."
Jenner is going, though.
For her the time is right to honour her colleagues and pay her respects to everyone who died. She hopes the 10th anniversary will act as a catalyst for people to move on.
"The world has changed a lot. The US has a different perspective on what happened now. But for me it is important to remember and to respect the people whose lives were lost."
After a few years back in New Zealand Jenner moved to London. She says it is home for now.
But New York is etched on her heart.
