The youngster was cutting grass in the forest near her home in Baitadi district, on the border with India, when she was attacked by the animal, said Bishnu Bahadur Karki, a local deputy superintendent of police.
"The locals found the body torn into pieces and eaten below the neck at the forest area yesterday," he told AFP.
Karki said three young girls and a 35-year-old pregnant woman had been killed in the weeks leading up to Wednesday's attack and police believed the same animal was responsible for all the deaths.
"The leopard has continuously been victimising and terrorising the people of Pancheshwor village. We requested the district forest office to allow us to kill it but they refused, saying that the law does not provide such permission," Karki told AFP.
"Our request to have the leopard handed over to a zoo has also been rejected. The villagers and police are trying hard to take that leopard into custody."
Villagers claim three more people have been killed by the leopard in nearby settlements on the Indian side of the border.
"We are scared to walk alone," Shiva Singh Saud, the headmistress of a local primary school was quoted as saying in the Kathmandu-based Republica newspaper.
"More people may be attacked if the leopard is not taken under control immediately."
Most of Nepal's leopards are found on the sub-equatorial plains of the southern Terai and in forested hill regions, where conflict with humans is a perennial problem.
Seven people were killed by leopards in the same district last year, Republica said.
And in October a leopard dragged away and killed a four-year-old boy in Bela village, in the mountains of central Nepal, just 40 kilometres (25 miles) east of Kathmandu.
The boy was the third villager in three months to be killed by a leopard.