Theresa Riggi is serving 16 years for killing her eight-year-old twins Austin and Luke and their five-year-old sister Cecilia at their Edinburgh home in August last year.
The 47-year-old is understood to have been injured at Cornton Vale Prison, near Stirling, when she was allegedly thrown down a flight of stairs on 22 October.
A female prisoner was arrested and charged in connection with the incident.
A Central Scotland Police spokeswoman said: “A 22-year-old woman will be reported to the procurator fiscal.” The force is also investigating a separate attack on Riggi on 19 November.
The spokeswoman added: “We can confirm that a 47-year-old woman was attacked in Cornton Vale Prison. Inquiries are ongoing.”
The bodies of Riggi’s three children were discovered at a townhouse in Slateford Road on 4 August last year following a gas explosion at the building.
Riggi, originally from the United States, was initially charged with murder but later jailed after admitting three counts of the reduced charge of culpable homicide on the grounds of diminished responsibility.
The court heard she had a “possessive love” for her children and had been involved in a custody battle with her estranged husband.
Passing sentence, judge Lord Bracadale told her that a “devastating family tragedy” had resulted from her actions.