But Ms Frew said she believed the explanation was full of "half truths". She said it minimised Mr Brider's involvement in her younger brother's death.
"If you're going to own up to something like that, own all of it," she said. "He sprinkled fairy dust around with his story, trying to get a feelgood story to cut a break."
Ms Frew's comments come as X Factor creator Simon Cowell revealed he was upset over Brider's appearance. Cowell's company, Syco, told the Herald's Diary: "We have latterly been made aware of the situation and take this matter very seriously. We are currently looking into it with the local producer, MediaWorks."
A clause in the contract held by Syco Entertainment and FremantleMedia, owners of the format, stipulates the show can't be brought into disrepute in accordance with the third-party license agreement.
It is understood that special dispensation would have needed to be sought to use Brider, and MediaWorks failed to get permission. A representative for Cowell said he had no knowledge a convicted killer was to appear on the show.
For Ms Frew and other family members, Mr Brider's appearance on the show dredged up painful memories from 10 years ago.
Jeremy and his friends had been parked at Castlecliff Beach after a party when Mr Brider and the other men approached and began punching Jeremy through the car window.
The attack ended when Jeremy screamed. A friend, who was in the car at the time, told the murder trial Jeremy then started the car and drove off, reaching Rangiora St dairy. Then Jeremy said he thought he had been stabbed.
He was not the only victim that night - Mr Brider and the other men travelled around the city in a "rampage of violence", prosecutors said at the trial.
There had been two assaults earlier in the evening on three other men, one of whom was also stabbed.
Ms Frew was watching X Factor with her partner when Mr Brider appeared. "I knew straight away," she said. She got up and walked out of the room, asking her partner to turn the TV off.
She was upset the show's producers hadn't contacted the family to warn them of Mr Brider's appearance.
Mr Brider, who has quit Wanganui for a new life in Masterton, said his X Factor appearance was about "tearing down another wall" to escape his past life.
"I've done everything I can to be respectful to the family. I took myself away from my home town in order to give them space, and I've never gone back there because of that. That's their right, their son was taken from them."
He also said Jeremy had been his friend, but Ms Frew said this was not true, and felt Mr Brider had not taken responsibility for his actions. "He tried to do the heartfelt story to gain sympathy ... not just from the audience but from the nation. Part of me can't help thinking that X Factor did it partially for ratings."
X Factor said Mr Brider disclosed his criminal record from the start. "It was important to include this part of Shae's background in last night's episode and this was done in his own words. The X Factor acknowledges the impact Shae's past actions have had on his victims, and apologises for any distress that has been caused."
Ms Frew pointed out Mr Brider had appealed the conviction and been re-tried, only to receive a longer sentence and have more evidence brought against him.
Yesterday MediaWorks spokeswoman Rachel Lorimer said the company wanted to apologise again for any distress or hurt caused.
"We take the impact it has had on the victim's family very seriously and have today been talking with (Jeremy's mother) Donna Travers, both to apologise personally and to discuss with her the best way to add to yesterday's public apology," Ms Lorimer said.
Sunday's and Monday's episodes would start with an apology to Donna and her family.
