The military said the girl was among 97 women and children held hostage by Boko Haram who were freed on Thursday after armed clashes in Borno state.
It said she was number 157 on a list of 218 students seized, but community leaders cast doubt on the claim, saying her surname suggested she was not one of the Chibok girls.
Amina Ali Darsha Nkeki, the first girl to be rescued, was found by soldiers working with a vigilante group on Tuesday in the remote area where Boko Haram has waged a seven-year insurgency to set up an Islamic state.
Officials confirmed 19-year-old Amina, pictured above with her four-month-old baby meeting Nigerian President Muhammadu Buhari on Thursday, was one of the girls abducted from a government school in Chibok in April 2014.
Their kidnap caused global outrage and led to the #BringBackOurGirls campaign on social media.
The governor of Borno state, where Chibok is located, said the army was drawing up plans to rescue the remaining girls.
Amina said six of the girls had died, but the rest were under heavy Boko Haram guard in Sambisa.
President Buhari said: “Amina’s rescue gives us new hope and offers a unique opportunity to vital information. Nobody in Nigeria should be put through the brutality of forced marriage, Every girl has a right to education and their choice of life. Amina must be able to go back to school.”
After Amina was discovered, the army said it had detained a suspected Boko Haram militant called Mohammed Hayatu, who said he was her husband.
President Buhari, Nigeria’s former military leader, made crushing Boko Haram a pillar of his 2015 election campaign.
Nigeria’s army has recaptured most of the territory seized by Boko Haram, but the jihadist group, which last year pledged loyalty to Islamic State, still regularly carries out suicide bombings.
It captured 276 girls in a night-time raid in Chibok two years ago, but several of them escaped.