Kindred by Octavia Butler (1979)
Dana, a Black woman who lives in the 1970s, suddenly finds herself time-traveling to 1819 Maryland. She is called upon to save the life of young Rufus, son of a hideous slave-owner and her white ancestor. This is repeated twice more (once with her white husband Kevin) to save the life of Rufus. Time passes in years in Maryland but hours and days in 1976.
Dana is engulfed in the life of slaves trying to provide care and comfort in a time of harshness and humiliation. Trying to make changes to slave treatment earns her a beating and she comes dangerously close to losing her life. Kevin working to help slaves escape finally returns after five years to Dana. She fights valiantly against possession by Rufus. Will she win? Will she return to 1976? Will she become a slave like her ancestors?