The girl, known as Spozhmai, said her brother and father had beaten her, ordering her to put on a suicide vest.
She was taken into protective custody in the provincial capital Lashkar Gah, after an Afghan soldier spotted her wearing the vest last Monday.
Said to be about 10, she has appealed to Afghan President Hamid Karzai to put her in a new home.
A presidential spokeswoman said she would only be returned to relatives if tribal elders guaranteed her safety.
The girl is thought to be the sister of a prominent Taliban commander, who police say encouraged her to carry out the attack.
She told the BBC's Newsday programme that she had been scared to carry out the attack, but that her brother had promised only her targets would die.
She added that her father had ordered her to return home, but she refused to obey.
"I said: 'No, I will kill myself rather than go with you'," she said.
"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.'"
The girl said she had not been allowed to learn to read and write.
"I did all the things at home, I cooked, I cleaned the whole house, and they would treat me badly as if I was a slave,"  Spozhmai said.
In her appeal to Mr Karzai last week, the child said: "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."
The president has condemned the Taliban over the incident, but the group has denied any involvement in the alleged plot.
An Afghan girl has told the BBC that her family forced her to attack a police checkpoint in Helmand province.