(CNN) -- The California runner who was lost in a forest for three days without water had barely a few hours to go before she would have died, her doctor said Thursday.
Runner Maria "Gina" Natero-Armenta, 36, survived for three days without water in a California forest.
Maria "Gina" Natero-Armento, 36, not only survived 72 hours with only a slice of apple in her stomach and a little bit of water for nourishment, she also has only one functioning kidney, Dr. Derrick Hong said.
He spoke with CNN on Thursday afternoon, along with Natero-Armento and her husband, Armando Armento, in a conference call interview from her room at Mission Hospital in Mission Viejo, California.
Natero-Armento is no amateur when it comes to distance or mountain running. She's one of the top female finishers in a San Diego 100-mile race and an experienced ultrarunner with top times in other 100-mile and 50-mile races. Her body was unusually strong to begin with, but she also has one kidney -- the other doesn't function because of a congenital disorder.
"This is extraordinary," Hung said.
She said she had planned a simple eight-mile run, a small fraction of what the ultrarunner usually tackles in a sport that challenges competitors to run at least farther than a 26.2-mile marathon. She is among the majority of ultrarunners who like doing 100-mile races.
She set out from her Oceanside home at 5:30 a.m. Sunday to meet Fidel Diaz, her running partner and brother-in-law, who is also a serious ultrarunner. They planned to run along a trail in the the Cleveland National Forest near San Diego.
She brought along two water bottles and wore a Camelpak, a backpack that can be filled with water. That was plenty of water for an eight-mile outing. She didn't bring food with her, but Natero-Armento said she ate a piece of apple before she started, and that was the only food in her stomach.
Natero-Armento said she did several things that were out of character that day, and she wishes she had been more prepared.
"I am very careful usually, but that particular day, I was not," she said. "I normally, the night before the long runs, I have everything ready. And this night, I had nothing ready, and it was just a mistake."
She usually wears a Garmin GPS watch, a sophisticated device that runners use to find out where they are, the distance they have traveled, calories burned and altitude.
"I didn't have my Garmin and wasn't wearing a watch," she said. "I don't know. I always carry food with me, and I didn't have nearly enough."
"I always carry my phone with me, and I didn't have my phone with me, and that really was a big mistake," she said. Feeling antsy to just get on the trail and run, she wasn't thinking deliberately. "I just wanted to get going that day; get some fresh air and go for a run. I hurried up."
Natero-Armento and Diaz began running about 6:30 a.m. Sunday, she said. She lost track of as much as eight hours, she said, as she and Diaz became lost. By then, she was dehydrated and disoriented.
And Natero-Armento said she also made another, more serious bad decision. At some point in the run, Diaz had become ill. Ultrarunning is a sport in which some participants sometimes push themselves way too hard.
"[He was] pretty much beside me or in front of me, but I do know that I was insisting on keeping going since I was OK," she said. "He doesn't eat or drink much ever [when out on runs], so I know he can handle that."
She said that she kept going because she'd seen him run hard while sick -- also not uncommon in 50- and 100-mile races -- and that she figured he could handle it if she pushed him.
She said they became separated as they two were going over a rugged hill.
"We had separated because we were going through a hill quite a while and had to go through brush, and that's how I have a lot of scrapes. So that was very difficult," she said. "[We] crawl under and break branches, and that was the only way we were going to get out of there, according to Fidel. So I don't think he was able to see that I was not there anymore."
She said that Diaz was in front of her. He would shout to her so they knew the other one was close by: He shouted to her, and she shouted back. Then, at one point, she couldn't hear him anymore.
"When I called him and he didn't answer, at this point, I lost a little bit of control," she said.
Night turned into day. She had no water or food, and she didn't try to eat anything. She became disoriented but had the wherewithal to know that she was completely out of fuel. She didn't have the strength to keep walking, so she climbed into a ravine, believing that would be the safest place.
Diaz was not available for an interview Thursday.
He was found Wednesday several hours before she was. It's not clear why he was lost for so long and where, for days, he had traveled in the forest.
Rather than ask for water, law enforcement said, Diaz asked how Natero-Armento was doing and if someone had found her.
"I really had to, from the beginning, accept that I was not capable of getting out of there, there was no where to go," she said, recalling her hours in the ravine, thinking about her husband and her family. She told herself she would live.
"I knew what I had to do."
The experience has not scared her away from distance running on trails. When her kidney is strong again, she will be back, running.