The body of Roshani Tiruwa was found by her father last weekend in a stone and mud hut in the village of Gajra, in Achham district, 440km (275 miles) west of Kathmandu.
The 15-year old is said to have suffocated after lighting a fire to keep warm.
The banishment is an ancient practice called chhaupadi, where women who have their periods or who have just given birth are seen as impure.
Some communities in remote areas believe that they will suffer a misfortune such as a natural disaster unless menstruating women are secluded. While in isolation they are denied their usual intake of food and are prohibited from drinking milk.
It was banned by the Nepalese government in 2005, but still continues in remote western rural areas.