Cowen was born in Britton, Lenawee County, Michigan, USA, on 13 September 1906. Her parents were Henry Martin Rambow (1875–1947) and Caroline J. Weilnau (1877–1964). She had three siblings, Earl Henry (1908– 1983), Ruth (1910–2014) and David (1912–2005).
Around 1929, she got married and moved to Texas with her husband. They first lived on a farm in West Bexar County. The couple had two daughters: Ruth Caroline and Louise Marie. She later worked in important business offices in San Antonio.
Her younger sister, Ruth Piotter, passed away on 13 December 2014, aged 104.
Cowen passed away in LaCoste, Medina County, Texas, USA, on 31 August 2018, at the age of 111 years, 352 days.
Her age was validated by LongeviQuest on 17 April 2023.