The lover of a woman murdered along with her family in Clydach, Swansea Valley, has denied the killings.
Alison Lewis gave evidence for a second day at Newport Crown Court
Under cross-examination, Alison Lewis told Newport Crown Court: "I'd have given my life to protect them and that's the truth".
David Morris, 44, of Craig-cefn-parc, denies murdering Mandy Power, 34, her daughters and her mother in 1999.
Ms Power, Katie, 10, Emily, eight, and Doris Dawson, 80, were beaten to death at their home, which was set on fire.
Giving evidence at the retrial of Mr Morris, Alison Lewis recalled how the day after she heard about the killings, she had gone to an upstairs room in her home, opened the window and attempted to throw herself out.
She was then admitted to a psychiatric unit for two weeks following the deaths suffering from "extreme grief reaction".
Ms Lewis and Ms Power had been involved in a lesbian relationship, the jury heard.
Former scrap metal dealer David Morris denies four murder charges
But although she made no attempt to hide the relationship around the Clydach area, Ms Lewis said she was convinced her husband, Stephen, had been unaware of it.
She admitted in court how she had acted in a "selfish, mean and spiteful" way towards her husband over the affair and had treated him with "selfish contempt" by bringing Ms Power back to the home she shared with him for sex.
Ms Lewis said that she was a jealous person but "no more jealous than anyone else in a relationship" and she denied disliking Ms Power's children.
The jury heard how nearly a year after the murders, Ms Lewis, her husband Stephen and his twin brother Stuart - both South Wales Police officers - were arrested and questioned in connection with the murders.
She told the court the police had come "to wrongly accuse her of murdering four people she said she would have given her life to protect".
During her evidence, she was asked by the barrister representing Mr Morris if she had been to Ms Power's house in Kelvin Road, Clydach, in the early hours of Sunday, June 27, 1999 - the night of the murders.
Mandy Power, her daughters and her mother were battered to death
She broke down as she denied the allegation and said her only guilt was while Ms Power was fighting for her life and that of her family, she was in bed asleep with her husband.
She said she was tired of being made a "scapegoat for the murders".
She said she was prepared to give another imprint of her hand and compare it to the bloody mark that was found in Ms Power's house following her death.
At the opening of the retrial in May, Patrick Harrington QC, prosecuting, said the family had been victims of the most appalling and grotesque violence - bludgeoned to death by a long pole
The trial continues.