Khadija Ibrahim, 30, told reporters she had been waiting for a bus to hospital in the north-eastern city of Maiduguri when she was seized by two men in a car who had offered her a lift.
While drugged, the mother of three was stripped and a suicide belt attached, she is quoted as saying.
She managed to flee her abductors.
Ms Ibrahim said after getting into the car, she fell unconscious when something was placed over her nose.
But she woke up, apparently without her captors realising, to hear one of them whispering to her that she was "going to do God's work".
The kidnappers told her she was being taken to the city of Kano to attack the Kantin Kwari textile market.
But when the car engine overheated, both kidnappers were distracted - one was examining the engine while the other went to look for water.
Ms Ibrahim then managed to flee and a man in the Hotoro neighbourhood of Kano took her to the police.
She was also brought before the Kano state governor, Umar Ganduje, who told the media: "If this woman had not regained consciousness the story would have been different by now."
The woman is now in "safe custody....undergoing post-traumatic rehabilitation," Kano police spokesman Magaji Musa Majiya told the BBC's Hausa service.
Police are trying to track down the vehicle in an attempt to find a second kidnapped girl, thought to be about 15 years old, he added.
The other woman in the car with her may also have been drugged, Ms Ibrahim suggested.
Boko Haram has staged numerous attacks using young women in the past year.