Reeva's mother, June Steenkamp, also revealed that she and her husband Barry were haunted by images of the shooting, for which Pistorius was sentenced to a five-year jail term.
June wrote in her new book, which is due to be released on November 6, that Reeva's clothes were packed, adding that there is no doubt in their minds that their daughter had decided to leave Pistorius that night, News.com.au reported.
June added that her daughter had confided to her that she had not slept with the runner and was scared to take the relationship to that level.
Pistorius, the first double amputee Paralympian to compete against able-bodied athletes at the 2012 London Olympics, said that he shot Steenkamp four times through a locked door to the bathroom in his Pretoria home because he mistakenly believed there was an intruder inside.
In Reeva: a Mother's Story, June wrote that she was shocked that the athlete was found guilty only of culpable homicide, or manslaughter.
June called Pistorius arrogant, moody, volatile and combustible, saying that he was a trigger-happy gun lover who was possessive of her daughter.
Proceeds from the book will help ease the family's financial difficulties, and help kick off fundraising efforts to set up a foundation for abused women in South Africa, according to the English-born mother.
June said that she thinks Reeva would have wanted them to have some money, adding that imagine going through this trauma, suffering, pain and having no money. But financial security will not ease the pain of losing a daughter, she added.