Puja Kermit Kakel (not official spelling), 46, was arrested after the teller at the booth filed a complaint with the Borphud police station.
Jindaporn Sikamut, 20, told police that a customer had arrived to exchange a wad of 20-pound notes at 3.30pm.
Jindaporn said she accepted the banknotes, which looked authentic and had light-reflecting watermarks. But she studied the notes more closely once the customer had left and discovered that four had the same serial number.
The Indian told police she purchased the notes innocently from an exchange firm in India before a trip to England, and they were left over from the trip.
Police refused to accept the explanation, saying she gave a fake name while exchanging the money and did not present her passport.