Patricia O'Connor's daughter told gardai when she was arrested: "You have someone for the murder."
He had "put his hands up", she added.
A Central Criminal Court jury heard when Louise O'Connor was arrested, initially on suspicion of killing her mother, she said she "didn't harm a hair on her head".
Her partner Kieran Greene had already been charged with murder after telling detectives he had killed Patricia (61), dismembered her body and dumped the remains in the Wicklow mountains.
"There's only two people who know what happened that day, me ma and Kieran," Louise said in interview. "Me ma's dead and Kieran's locked up."
Four people are on trial over Ms O'Connor's death - Mr Greene (34) is charged with her murder, while Louise O'Connor (41), her daughter Stephanie (22) and Louise's ex-partner Keith Johnston (43) are accused of impeding the investigation. They all deny the charges.
Ms O'Connor, a grandmother-of-seven, was allegedly murdered on May 29, 2017, at the house at Mountain View Park, Rathfarnham, she shared with family including her daughter, granddaughter Stephanie and Mr Greene.
Her remains were found scattered in the Dublin and Wicklow mountains between June 10 and 14 that year.
The charge against Stephanie O'Connor is that she disguised herself as her grandmother on the night of the alleged murder to pretend that Patricia was still alive, while her mother Louise is accused of agreeing to this.
The jury heard Louise O'Connor was taken to Bray Garda Station on September 2, 2017, and asked if she understood why she was being arrested.
"Not really," she replied.
"For the murder? You have someone for the murder. Put his hands up. Not really. You have the daughter here.
"I never raised a finger to her, never in my life," she added.
She told gardai she had gone out to Nutgrove Park with her children and father on the evening of May 29, before her mother went missing.
"Two weeks later we found out Kieran was after killing her," she said.
Ms O'Connor did not see her mother leave but heard her shouting and the door slamming, she said.
She was in the bathroom and she went out to see her mother "down the end of the road", having turned left.
She said before her mother left, she had shouted: "I'll be back when that b*****d pops his clogs".
She also said she had "a case or something" with her.
Louise went back into the house, put her children to bed and slept in her boys' room, she said.
She did not hear her mother come back, or anything after she went to bed.
"Kieran put his hands up to what he done," she said.
"There's only two people who know what happened that day, me ma and Kieran. Me ma's dead and Kieran's locked up.
"I understand how bad the situation got; I don't understand why he did what he did.
"I can't understand why he didn't get an ambulance, why he didn't call the guards. I didn't harm a hair on her head, I never did.
"I will go to my grave knowing I didn't harm a hair on her head."
Gardai asked if she had any suspicion that Mr Greene might harm her mother.
"No suspicion of murder. I knew something bad might happen. I was begging for us all to leave, for the council to give us a house. I never thought it would come to that," she said.
She was asked if she had her suspicions when her mother was missing that something had happened to her.
"In the house? No. After she left the house? Yeah," she said, adding that her brother and one of her children's birthdays had passed in the following days with "no contact from her. I started to get worried".
In another interview, she was shown footage of her house taken by a neighbour's CCTV on May 29. A person seen leaving with a suitcase at 9.43pm "looks like my ma walking out of the garden", she said.
She and her family were in the house that night, although her father Gus O'Connell did not return until later. He was seen at 10.23pm.
She was asked to identify a person seen coming in the back door at 10.05pm. They were carrying a "beach bag", she said.
"I haven't a clue who that is. It could have been Stephanie, me or Kieran," she told gardai.
The trial continues.