Rosemary Pearson said she thought it was a sick joke by a friend who phoned her - she only realised the horror when she turned on her television.
The American moved to the UK from Long Island 13 years ago and runs the Manhattan Gallery in Nottingham.
On Wednesday a memorial service at St Barnabas Cathedral in the city will remember her godson John Wallice, a 43-year-old father-of-three, and everyone who lost their lives.
One year on, Ms Pearson remembers a friend phoning her on that Tuesday afternoon.
"I must say I didn't believe him. I said 'please if this is a joke don't do this' and he said 'please just get to a TV set'.
"There was something terribly surreal about it but because John was in it, because I knew somebody in it, it was probably more real to me."
Her godson was a stockbrocker in the World Trade Center.
Ms Pearson said: "If he were my son I would be so proud of him that I could hardly talk about it.
"He was one of the finest young men I have ever known.
"I want every one of those people, whether they are Americans or not, to be remembered because it is probably the worst thing that I have seen in my lifetime.
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