Aine Adams, 40, who has waived her right to anonymity, said claims that her father Liam raped and abused her from age four had left her mother heartbroken and she did not want to cause further anguish.
She said although they were among the most vivid memories, when she first reported the abuse in 1987 she did not tell police about specific incidents including a rape allegedly carried out while her mother was giving birth. She later retracted the allegations that year.
Ms Adams told a court yesterday: "I have never told mummy the details of what happened. It would be hard for any mother – they are giving birth, and their husband is raping their daughter. As a 13-year-old, I thought I was doing the right thing."
Liam Adams, 57, from west Belfast, denies 10 counts of child sex abuse including rape, indecent assault and gross indecency. The trial at Belfast Crown court continues.