The founder of Nagoya Women's University, she was one of the first group of women elected to the House of Representatives in 1946,[1] Koshihara was born in the village of Oppara in Kamo District of Gifu Prefecture (now part of Higashishirakawa).
She joined the preparatory school of Waseda University in 1909 and graduated from its department of Japanese, Chinese and History in 1913.
She did not run for re-election in the 1947 elections, and in 1948 became principal of Nagoya Jogakuin Junior High School.
In 1950 was appointed president of Nagoya Women's Junior College [ja] and was awarded a blue Medals of Honor in 1958.
She died the following year, and was posthumously awarded the Order of the Sacred Treasure.