The 10-year-old girl, identified only as Spozhmai, was discovered Sunday near a police checkpoint in the Khan Nasheen district of Helmand province wearing the device.
She told soldiers at the checkpoint her brother and father beat her and forced her to wear the vest, the BBC reported.
Police believe Spozhmai is the sister of prominent Taliban commander identified as Zahir.
The girl told the BBC her father ordered her to return home but she refused.
"The same thing will happen again. They have told me before: 'If you don't do it this time, we will make you do it again,'" she said.
Spozhmai said she was never taught to read or write and was forced to cook and clean "and they would treat me badly as if I was a slave."
"I won't go back there. God didn't make me to become a suicide bomber. I ask the president to put me in a good place," she said.
A spokeswoman for the president said the girl would only be returned to her family if tribal elders could guarantee her safety.