Police search and rescue co ordinator Sergeant Aaron Nicholson told the Otago Daily Times yesterday she needed to negotiate the flooded track to get to her destination, the Young hut.
''She didn't cross the river.
''She hasn't made a bad decision to cross the river.
''She's just been walking the track and gotten to bits where the river has swelled over the track quite significantly.
''So she's had to negotiate that.
''So I would anticipate a realistic situation where she has fallen or tripped or slipped into that water.''
Miss Willen's body was recovered from the Young River, in the Mt Aspiring National Park, on Saturday.
Wanaka Land Search and Rescue volunteers found her body near where her backpack and raincoat were located in the headwaters of the river last Monday.
Miss Willen went missing after crossing the Gillespie Pass with two other young American female students in torrential rain, hail and gale force winds.
Asked why she and her two companions were not travelling as a group after crossing the pass, Sgt Nicholson said, ''sometimes tramping parties split up''.
''It is what it is, and everyone will be reflecting on what was involved and some of the rationale behind those decisions''.
He declined to comment further.
Miss Willen was spending a semester at the University of Otago, and had previously been studying human development at Eckard College in St Petersburg, Florida.
In a statement to the Northeast Ohio Media Group on Friday, dean of students Jim Annarelli said Miss Willen had organised community service projects for the college.
''Few can rival the seriousness of her approach to her studies, her commitment to the service of others both here and abroad, her sweet and caring personality, and her incredible enthusiasm and zest for life.''
Miss Willen had spent month long stints volunteering at orphanages in Tanzania, Guatemala and Malawi.
Her mother, Michelle Willen, described her as ''an old soul''.
''I know that she's gone and it's just her body, but it's a body that I loved for 20 years.''
Earlier this year, Miss Willen wrote in the University of Otago student magazine Critic, of completing the Kepler Track.
''My knees still ache, and I waddle to class with swollen feet.
''Completing my first Great Walk, the Kepler Track, was as beautiful as it was painful.
''I came to New Zealand with intentions of answering each invitation with a firm `yes' because I didn't want to miss out on any adventures during my semester abroad.''
Miss Willen wrote of her pride in completing the Kepler.
''Never again would I be so interconnected with that particular mountain, and I refused to allow pain or a bad attitude to taint my experience.''
And she wrote she was looking forward to her next tramping trip.
''I feel a more genuine sense of confidence about my next Great Walk. I will be equipped with a new type of mental strength I did not know I was capable of.''
Sgt Nicholson said Miss Willen's father, who had flown to Wanaka, expressed his family's thanks to search and rescue volunteers who had spent four days searching.
A team of 20 specialist land and marine search and rescue teams, including the coastguard, were involved in Saturday's search.
Sgt Nicholson said those involved were ''very pleased'' to be able to provide some comfort and closure for the family.
Police have referred the death to the Coroner for further investigation.
Almost two weeks ago, the body of German tramper Christine Lenicker (38) was found on the western side of the Homer Tunnel car park after snow had melted.
Earlier last month, American tramper David Tamowski (55) was found alive in the Routeburn area two days after being reported missing.
In January, the body of missing Wellington tramper Scott Oliver (41) was found alongside the Wilkin River in Mt Aspiring National Park west of Makarora. He had left a family tramping party on a track in the upper reaches of the river to take a shortcut through a gorge.
In May last year, Indonesian woman Yessica Asmin (22), who was visiting from Sydney, died when she was swept away while crossing a swollen creek on the Milford Track.
