In Nepali language, chhaupadi means someone who bears an impurity. Menstruating women are considered polluted, even toxic, and from the earliest age, people here are taught that any contact with a menstruating woman will bring bad luck.

An oppressive tradition has evolved around this taboo, including the construction of a separate hut for menstruating women to retreat to at night and then sleep in. Some of the spaces are as tiny as a closet, walls made of mud or rock, basically menstruation foxholes. Each year, at least one woman, usually more, and often young, dies in such a tiny space from smoke inhalation, a snake bite or exposure to the cold.

On Dec. 2, it happened again.

Shortly after sunrise, according to police officials, relatives of Parbati Budha, 21, sensed that something was wrong. Ms. Budha, who lived in a mountain village about a two-day drive from the capital, Kathmandu, was usually an early riser. She was known in the village as a determined worker who was quite bright; she graduated from 12th grade, unusual for girls from her village.

But on this morning, she did not emerge from her chhaupadi hut. When her sister-in-law and brother-in-law went to check on her, they found her on the shed’s floor, face down. Investigators said she had built a small fire inside the hut to keep warm during the freezing night, and died from inhaling too much smoke.

Ms. Budha had married about a year and a half ago and moved in with her husband’s family, as most women do in rural Nepal. Her husband worked in a sari showroom in neighboring India, and police officials say it was her husband’s brother, Chhatra Raut, 25, who pressured Ms. Budha to move out to the shed. (Some police officials said his name was Chhatra Rawat.)

The news about Ms. Budha’s death quickly spread, dismaying human rights activists. The activists, including Ms. Kunwar, asked the local police to investigate, but the officers refused. The officers said that nobody in the village had complained about the young woman’s death and therefore there was no case.

But the activists kept up their pressure. And in Kathmandu, the tide has turned against chhaupadi, which has become something of an embarrassment to those trying to modernize Nepal.