Her uncle has described her as pregnant and traumatised but otherwise fine.
Amina Ali Nkeki is the first of the 219 Chibok girls to escape from her captors since their abduction grabbed worldwide attention more than two years ago.
She was found wandering in the forest, her uncle Yakubu Nkeki said. He said the 19-year-old – she was 17 when she was abducted – was taken to Chibok on Tuesday night for her identity to be verified and to be reunited with her mother. Her father died while she was held captive, he said.
He said the soldiers then took the young woman away, apparently to a military camp in the town of Damboa.
Other Chibok girls may also have been rescued by soldiers hunting down Boko Haram in the remote northeastern Sambisa Forest on Tuesday night, said Chibok community leader Pogu Bitrus. He said he is working with officials to establish their identities.
Boko Haram Islamic extremists stormed and firebombed the Government Girls Secondary School at Chibok on April 14, 2014, and seized 276 girls who were preparing to write science exams. Dozens escaped in the first hours, but 219 remained missing.
The inability of Nigeria’s government and military to rescue them led, in part, to the electoral defeat of President Goodluck Jonathan last year.
It’s not known how many thousands of girls, boys and young women have been kidnapped by Boko Haram in a nearly seven-year-old insurgency that has killed some 20,000 people and spread across Nigeria’s borders.
Nigeria’s military has reported freeing thousands this year as they have forced the extremists from towns and into strongholds in the sprawling Sambisa Forest. Boko Haram has turned to soft targets using suicide bombers.
A video broadcast in April this year appeared to show some of the kidnapped schoolgirls alive.
Fifteen girls in black robes were pictured. They said they were being treated well but wanted to be with their families.
The video was allegedly shot on Christmas Day 2015 and some of the girls were identified by their parents.
The Chibok schoolgirls, many of whom are Christian, had previously not been seen since May 2014, when Boko Haram released a video of about 130 of them gathered together reciting the Koran.
Their abduction led to the #BringBackOurGirls campaign, that was supported by US First Lady Michelle Obama and Pakistani activist Malala Yousafzai.
The US, UK and France have been providing military support and intelligence to help in the search for the girls.
China and Israel have also given assistance.
A regional force with 8,700 troops from Cameroon, Chad, Niger and Nigeria was launched last July.
Thousands of people have been freed from Boko Haram captivity, but Amina is the first of the 219 girls to be found.