It was her first tramping trip in New Zealand.
"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," Ms Willen wrote.
Climbing to the highest peak of the track, at 1400 metres, gave Ms Willen blisters and muscles cramps but also taught her "more about myself than I thought was possible", she wrote.
She described the landscape as gorgeous and said it would be her only chance to soak in the views on the Kepler Track.
She was looking forward to more tramping in the future.
"Before leaving, I laid in the grass and felt a sort of bliss and pride that I had never before experienced.
"Kepler taught me that our limits exist only because we create them, and 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."
Several of Ms Willen's friends have commented and shared the column since news spread that she was missing.
Kevin James Karas, of Ohio, commented that the words reminded him of good times spent with Ms Willen.
"You are such an inspiration to my life, I feel so connected to every word of this article on so many levels, it reminds me of our deep talks together..." he wrote.
Ms Willen was found in the Young Valley river by one of 20 specialist Land and Marine SAR teams involved in the search, shortly before lunch time yesterday, high in the Young Valley, he said.
"We had waited for three days after our initial search effort for the water levels in the Young Valley to recede to an optimum searching level," search coordinator Sergeant Aaron Nicholson said last night.
Her family had been advised and were "very relieved to have Ally back", Mr Nicholson said.
The death has been referred to the coroner.