Milner was also sentenced to six years in prison for attempted murder, to be served concurrently.
Helen Milner, 50, was found guilty of murdering her second husband Phil Nisbet by poisoning him with a sedative and finishing him off by suffocating him with a pillow in 2009.
She was found guilty by a jury in the High Court at Christchurch in December.
The 47-year-old truck driver's death was initially ruled as a suicide, but a homicide investigation was launched two years later after a coroner raised doubts.
Mr Nisbet's sister Lee-Ann Cartier became sceptical of Milner's story within days of her brother's funeral and, from her home in Queensland, did her own detective work and supplied information to police. Her digging led to Christchurch police reopening the investigation.
