Born in Nebraska, the fourth of nine children born to Katarina and Bernhard Kroeker, German Russian immigrants.

She grew up near Henderson and lived in Colorado and Texas with her family. Her father, Bernhard, was a farmer and minister with the Evangelical Mennonite church.

The life-changing event in Sarah's life was the Galveston Hurricane of 1900. Her family had recently moved to a new Mennonite settlement around Richmond, TX. She was 18 when the storm hit their community, and her mother died as a result. She remained a few more years in Texas, until after her father re-married and she was no longer needed to care for the family. Forty years later she wrote a detailed account of her own experiences in the storm.

She went on to McPherson College in Kansas to study Bible. For a time she lived in Chicago with her older sister Katherine (Kroeker) Wiens, and helped in various nursing and childcare capacities, as well as with the Mennonite Mission there.

In 1912 she felt the call to go into missions in Africa. She traveled to London, where she lived for seven months training in nursing and midwifery. While there she nursed premature triplets back to health, and returned them to their family.

Sarah arrived in Djoko Punda, Congo on January 24, 1913, sent by the Congo Inland Mission of the Mennonite Church. She then transferred to the Kalamba mission station. On April 26, 1915, she transferred back to Djoko Punda, where she met Swedish medical doctor and missionary, Oskar Andersson, who had arrived earlier. He joked that he fell in love with her "big boots" when she first stepped off the train. She was wearing hand-me-downs from a deceased elderly male patient, having lost most of her other clothing right before traveling.

German was the language which brought Sarah and Oskar together,as well as their love of Jesus and their commitment to service and witness to the people of the Congo.They were married on September 14, 1915. Some of these experiences are inscribed in a book written by their great-neice Helen Coon, called "Oskar and Sarah: a Congo Love Story" (no longer in print).

In 1916, a son was born to them, and died during a long and complicated birth. Later they lost twin children as a result of miscarriage. She reported several other miscarriages. They had no biological children who survived. Oskar and Sarah raised at least 18 (known) children during their mission years, and Sarah became known as "Mama Sarah". Most were children considered unwanted, who might have been left alone to die.

She and Oskar moved back to Sweden in 1948. In 1969 she passed away and was buried in Sweden. Oskar placed a single rose on her grave every year on her birthday, before he too passed away.