Senior Constable Barry Shepherd was part of the team which found the woman at 8.30am yesterday.
"She was halfway down the east side [of Ngauruhoe] going the wrong way," Mr Shepherd said.
She was airlifted by the Taupo-based Greenlea Rescue Helicopter and taken to Whakapapa Village before continuing to Taupo Hospital. Mr Shepherd believed the woman had a sprained ankle but was not suffering hypothermia.
The woman's group "lost sight of her at the staircase leading out of Mangatepopo valley crater," Mr Shepherd said.
"She went right to the summit and over the top and down the other side.
"We responded with the rescue helicopter just before dark and did a search of all tracks with night vision goggles, then put a search team on the summit of Tongariro. The police call-taker at Communications couldn't determine where she was.
"Her and her friends speak good English - but she was seriously upset. It was a challenge for the call-taker to reach her."
As she climbed Mt Ngauruhoe the woman had been spotted by another tramping party. They told the Mangatepopo Hut ranger, who finally alerted rescuers to the woman's location.
Mr Shepherd said the woman "is obviously quite resilient" as the temperature dropped to 1C overnight: "She was wearing a T-shirt, hoodie and yoga pants, pink cap, blue backpack. We were surprised she was in such good condition [yesterday]."