Terhune's first writings, written under a more masculine pseudonym when she was 14, were evangelical essays for the "Watchman and Observer", a weekly religious paper. Starting with the publication of her first novel, "Alone", in 1855, she became one of the top-selling authors of women's fiction. Her early novels all featured a romantic story element, with many also including "sensational episodes-murders, fires, accidents, and sudden deaths." The works explored a variety of topics, with earlier works looking at the "domestic and religious lives of young women" and later works delving into depravity, alcoholism, drug addiction, and mental illness. Literary critics at the time classified her as a "plantation novelist". Since the late 20th century, critics have appraised her differently, noting that Terhune set several novels outside of the South, including two set in New York City. They also noted that she was critical of various social institutions considered acceptable in the antebellum South, including slavery and marriages between close relatives.