Sibonglie Dube, 19, and Kiran Mahmood, 18, were locked up for two years on Friday for the robbery of Mohammed Fayyaz.
He picked the girls up from outside the Moon Under Water pub, in Watford High Street, at around 10pm night on August 22, St Albans crown court heard.
Prosecutor David Chrimes said: "Both had scarves on their heads and scarves on the lower part of their faces. The only part of their faces that were visible were the eyes and nose."
Dube got into the front of the taxi and Mahmood was in the back seat. They told Mr Fayyaz they wanted to go to an address in West Watford but on the way, Dube told him to drive to Shepherds Road, a dark dead end next to Cassiobury Park.
Mr Fayyaz said the fare was £4.80. He though Dube was about to pay when she said: "Give me all your money."
She told Mahmood, who had put either her fingers or a toothbrush against his shoulder, to shoot him, said Mr Chrimes.
He handed over a total of £44 from various locations in his cab. They left with Mahmood taking the victim’s car keys.
Mr Chrimes said the taxi driver was left "traumatised" by his ordeal.
Forty minutes after the robbery, the two girls were spotted by the police as they walked along Rickmansworth Road. Dube told the officers they had found the taxi’s keys on the road.
But when questioned both made full and frank admissions to the police, said the prosecutor.
Dube, of Grampian House, Edmonton, and Mahmood, of Harebreaks, Watford, pleaded guilty to robbery. Neither girl had any previous convictions or cautions.
Dube said her mother was returning with her to Zimbabwe and she wanted to get money together to return to the UK.
Mahmood, who was said to come from a hard-working Muslim family, said she felt so bad about the robbery as her own grandfather worked in Watford as a taxi driver.
Recorder Gordon Reed said the offence was so serious that only a custodial sentence could be passed. –watfordobserver