The course took in the pick of the sights of Westminster and the City of London, including a short indoor section through Leadenhall Market.
"I have never run a course like that," she said. Asked if she would have tailored her preparation any differently if she had her time again, Smith said she would have practiced her tight turns more as she kept losing time on the twisty section.
"I just felt terrible. I really struggled in the parts with the turns. From the start I was losing ground through there."
Smith, 30, wanted a top six finish. Anything less, despite having a comparatively small body of work behind her at this distance, she must have felt was not doing justice to her talent, hence her disappointment.
She remained in a large lead group dominated by the Kenyans and Ethiopians until the halfway mark, when her splits for 5kms rocketed from around 17 minutes flat to 17m 40s. She battled on to the finish and was starting to pick up a couple of places by the finish line.
"The crowd support was amazing," Smith, who had her parents and fiancée in the crowd, said. "I've had nothing like that before; there was a lot of New Zealand support."
Smith was hoping to emulate the feats of Barry Magee (bronze, Rome, 1960), Mike Ryan (bronze, Mexico City, 1968), and Lorraine Moller (bronze, Barcelona, 1992) as New Zealanders to have won medals at this event.
She will now have to wait until Rio de Janeiro to achieve that goal, hopefully on a course more to her liking.
She will only have to wait three weeks until her next really big day however. She marries fellow athlete Patrick Tarpy in Maine, USA, in three weeks.