The convicted killer dubbed the "Black Widow" has reportedly been attacked by two inmates.
Helen Milner, 52, was punched in the face and other parts of her body at Arohata Prison yesterday, Stuff.co.nz reported.
When contacted by the Herald tonight, Arohata Prison director Chris Burns confirmed that "a female prisoner" was assaulted yesterday.
"The assault was not serious and no injuries were sustained," he said.
"Corrections is investigating the incident, and the prisoner will have the opportunity to speak with Police.
"Corrections manages some of New Zealand's most difficult and challenging citizens, and many offenders resort to violent behaviour as a means of resolving issues," Mr Burns said.
Milner was arrested in October 2011 with the murder of her husband, Philip James Nisbet, 47, in Christchurch in 2009.
Police initially believed the death was a suicide.
She is serving a life sentence with a minimum non-parole period of 17 years.
The court was told Milner poisoned Nisbet by lacing his dinner with the sedative drug Phenergan.
Milner has maintained her innocence.
