The 18-year-old girl, identified only as Lubna, was arrested at the weekend in the troubled northwestern city of Peshawar after a trader complained to police.
Furqan Bilal, a senior police official, told AFP the trader said he received a phone call from an "anonymous militant" demanding millions of rupees.
The caller threatened to kidnap the trader's children if he did not pay up, Bilal said.
"We began an investigation, traced the number and came to know that up to 10 people have been threatened using the same number," Bilal said.
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"The girl was more clever than we first thought -- she was using a voice modifier and was constantly changing SIM cards and even mobile handsets," Bilal said.
None of the intended victims of Lubna, a student at a college in Peshawar, paid up. But she did manage to cash a cheque for one million rupees (USD 9,820) that she had stolen from her brother-in-law, police said.
Peshawar has suffered the brunt of the Islamist violence that has swept Pakistan in recent years, much of it perpetrated by the Tehreek-e-Taliban Pakistan (TTP), and militant groups often kidnap for ransom to raise funds.
"The girl has confessed to making threatening calls using the Taliban name," Bilal said.
"She also confessed that she was doing this to extort money."
A court in Peshawar yesterday ordered that the girl be remanded in custody for 14 days.
Mian Saeed, another police official confirmed the arrest and told AFP she was "apparently inspired by local TV crime shows and dramas".