Complex sentence: In 1913, Sinclair married Mary Craig Kimbrough (1883--1961), a woman from an elite Greenwood, Mississippi, family who had written articles and a book on Winnie Davis, the daughter of Confederate States of America President Jefferson Davis.
Split into simpler sentences: In 1913, Sinclair married Mary Craig Kimbrough (1883--1961), a woman from an elite Greenwood, Mississippi, family. She had written articles and a book on Winnie Davis, the daughter of Confederate States of America President Jefferson Davis.