Nemcova was just as sure at first that her fiancé had lived – "he was such a strong swimmer, of course he'd survive" – but there was to be no happy reunion story for her.
This year, Nemcova is returning to Thailand for a candle-lighting ceremony to commemorate the 10th anniversary of the disaster, but it is not the suffering and loss she will be marking.
Her fiancé Simon Atlee, a British fashion photographer, was missing, swept away by the crushing deluge that engulfed their beach bungalow.
Nemcova briefly saw Atlee for what would turn out to be the final time as she desperately tried to cling to the roof of building and gasped for breath, while all around her, the roar of the water was punctuated by screams.
The sea swept back out and then rushed ashore in a second colossal wave, dragging Nemcova underwater again.
"This time, I couldn't get back above the surface to breathe, there was so much debris above me.
I started swallowing this toxic water and I thought 'this is it'.
"They'd gone." Nemcova spent eight hours there, first clinging to the tree and then lying amid the mud and debris when the water finally receded, unable to walk, passing in and out of consciousness under the hot sun, her pelvis shattered in four places, as she would later learn.