She was discovered by soldiers investigating suspected members of Islamist militant group Boko Haram.
Nigeria's military said the young woman is undergoing medical checks.
A total of 276 schoolgirls were kidnapped by Boko Haram from the town of Chibok in April 2014. About 200 of them are still in captivity.
More than 20 were released in October in a deal brokered by the International Red Cross. Others have escaped or been rescued.
Over Christmas, 21 of the young women freed under the October deal returned home for the first time.
However, family members told the BBC that they were kept in a politician's house and barred from going to their family homes.
A statement from the office of state governor Kashim Shettima acknowledged that "armed soldiers... escorted the 21 girls to Chibok and remain their strict guards throughout Christmas".
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Prior to this, the girls had reportedly been held in a secret location for debriefing by the Nigerian government.
Two weeks ago, Nigeria's President Muhammadu Buhari said the army had driven Boko Haram's militants from the last camp in their Sambisa forest stronghold in north-eastern Nigeria.
"The terrorists are on the run and no longer have a place to hide," Mr Buhari said in a statement.
Boko Haram has killed 15,000 people and displaced over two million during its seven-year battle to create an Islamic caliphate in the north-east of the country.

Morgan Geyser and Anissa Weier have been charged with attempted murder over the attack.
Last week, a Wisconsin judge decided that they should be tried as adults, meaning they could face decades in jail if convicted.
The victim, 12 at the time, was stabbed 19 times but survived.
She was found by a cyclist crawling from the woods where she was attacked with stab wounds to her arms, legs and torso, after the attack in May 2014.
A judge entered not guilty pleas on behalf of both girls at a hearing on Friday.
Investigators say the two girls had been plotting for months to kill their victim in "dedication" to Slender Man, a fictional horror website character.
They spoke of their desire to become the paranormal figure's "proxies" by killing to demonstrate their loyalty, police said.
A lawyer for one of the girls told the AP news agency before the hearing that his client would enter a plea of not guilty by reason of mental disease or defect.
Their lawyers have previously argued for the case to be heard in juvenile court, saying both teenagers were suffering from mental illness.
Following the attack, the suspects were found walking near a local highway and a knife was found in one of their backpacks.
The victim has recovered and since returned to school.

Cambridgeshire and Peterborough Combined Authority (CPCC), set up this year, originally estimated annual running costs of about £1.3m.
But the authority's scrutiny committee voted against approving it, with one member asking if recruitment plans were "written on the back of a bus ticket".
CPCC said a reason for the rise was that a new authority was being created.
The authority, created under government devolution plans, intends to employ 15 staff, including newly-created housing, skills and transport director roles all on annual salaries above £100,000.
After Wednesday's decision by the scrutiny committee, the process of recruiting any new staff cannot begin until CPCC has reconsidered its budget, the deadline for which is 31 August.
Labour Cambridge city councillor Dave Baigent, a member of the scrutiny committee, asked of the new jobs: "Were these ideas written down on the back of a bus ticket? Were they discussed with councillors in advance?"
Lucy Nethsinga, a Liberal Democrat county councillor, said she had concerns over how these jobs overlapped with those in county and district councils.
CPCC chief executive Martin Whiteley said: "We, with 15 staff, will be substantially smaller than any other devolved authority in the country.
"I don't envisage us creating a big shiny office. We'll be looking to work flexibly across council offices."
The Nigerian army says that one of the abducted Chibok schoolgirls has been found, along with her six-month-old baby.
[NEXT_CONCEPT]
Two 13-year-old girls accused of stabbing a classmate to please the online horror character Slender Man have pleaded not guilty in court.
[NEXT_CONCEPT]
A new devolved authority has been ordered to review its estimated budget after it rose by £500,000.