At an inquest in Queenstown yesterday, Otago Southland coroner David Crerar heard evidence from police search and rescue co ordinator Sergeant Aaron Nicholson, of Wanaka, that the most likely scenario was the 20 year old had slipped and fallen into a flooded Young River.
Ms Willen, also known as Ally, was found dead in the Young Valley northwest of Makarora on May 2, having become separated from her tramping party on the Gillespie Pass, between the Young and Wilkin Valleys, on April 25.
From Akron, Ohio, she had been studying at the University of Otago on an International Studies Abroad programme.
Sgt Nicholson said Ms Willen had limited tramping experience, and the trio collectively lacked the experience to deal with the situation they encountered between their lunch stop at Siberia Hut and their destination, Young Hut.
It appeared she had fallen while trying to follow the track, which was underwater, or while negotiating ground above the flooded river.
The flooding meant her body was not found by searchers until a week after she went missing. A postmortem concluded she suffered a head injury and drowned.
Ms Willen's two companions and fellow exchange students, Ellen Stone and Kirsten Kampmeier (both 20), now live in the United States and did not attend the inquest, nor was Ms Willen's family represented.
However, written statements from both women described how the trio became separated as a result of their different walking speeds, fatigue and deteriorating weather.
Ms Stone said she had ''never felt wind so strong in my life'' and often had to drop to her knees or on to her back to avoid being blown over.
Walking the same route that day were three American men, also exchange students at the University of Otago.
One of them, Caleb Irvine, said in a written statement that conditions were ''incredibly windy'' on the Young Valley side of the pass and the girls' failure to keep together was a ''poor decision''.
When darkness fell and Ms Willen had yet to arrive at Young Hut, the trampers agreed it was too dangerous to climb back to the pass to look for her.
Mr Crerar's formal written finding was reserved.
