Angela Hamilton is alleged to have disfigured Riggi for life by cutting her face with the blade.
She allegedly pulled the child killer's hair and repeatedly struck her face and head with the razor.
The alleged attack took place in Riggi's cell, at Cornton Vale Prison, near Stirling, on 19 November 2011.
Riggi, 49, originally from California, United States, who is serving 16 years at the prison, after admitting to stabbing her three young children at their home in west Edinburgh, had to be taken to hospital after the attack.
Hamilton, 40, denied the charge against her and is set to stand trial by jury at Falkirk Sheriff Court next week.
Theresa Riggi killed her three children, eight-year-old twins Austin and Luke, and their sister Cecilia, five, in August 2010, stabbing each of them eight times.
She then allegedly tried to cover up their deaths with a gas explosion, before trying to kill herself by leaping out of their second-floor flat
She had moved to Edinburgh with her children from Skene, Aberdeenshire, following the break-up of her marriage to the children's father, Pasquale Riggi.
The High Court in Edinburgh heard that Riggi had been a protective mother who was involved in a custody battle with her estranged husband over access to the children.
Riggi was originally charged with murder but later admitted culpable homicide on the grounds of diminished responsibility.
Lord Bracadale described the killings as "truly disturbing" and "grotesque".
Another inmate in Cornton Vale, a 22-year-old woman, was charged with assaulting Riggi last October by allegedly throwing her down a flight of stairs, but the case was dropped in June when the Crown Office said there was insufficient evidence.
A woman is to stand trial accused of slashing child-killer Theresa Riggi with a razor blade in Scotland's only all-female prison.