Margaret Archer appeared in the South Australian District Court on Friday after earlier pleading guilty to one count of assisting an offender - her son, Neil Archer.

The latter is serving a head sentence of life in prison and a 22-year non-parole period for the murder of 20-year-old mother Jody Meyers whose body was found under a concrete slab in August 2015.

In her victim impact statement, Sarah Meyers, the dead woman's sister, asked why Margaret Archer had concealed the crimes of her son.

"My question is why? Why couldn't you have told what you knew?" she said.

She said Archer had forfeited any right to a relationship with Neil Archer and Jody Meyers' son.

After a family barbecue, Neil Archer strangled Ms Meyers after a heated argument sparked by his concerns her family was trying to break them up.

He took her body to his parents' home near Mannum, east of Adelaide, and buried it under the floor of the toolshed before returning the next day to cover the grave with fresh concrete.

Archer then told police and the media she had "just taken off".

It was previously alleged his mother used the dead woman's bank card to steal $250 from her account, which she used to buy the concrete to cover Ms Meyers' body.

She had been missing for a month before police found her body.

Also addressing Archer on Friday, Tania Parsons, another sister, described Jody as a gentle, kind and caring person.

"I, like most others that knew her, adored her," she said.

"But like any person, she made mistakes - and her biggest was meeting your family."

Outside court, the murder victim's brother-in-law Michael Bates said Archer was "a monster, just like her son".

"If she'd come clean, Jody wouldn't have been missing for a month, we wouldn't have been sitting around for a month, we wouldn't have had to have all those emotions," he said.

Archer was remanded in custody to appear again in court next week.

National domestic violence helpline: 1800 737 732 or 1800RESPECT. In an emergency call triple-zero.

Australian Associated Press