Helen Milner, 50, had two previous convictions before she was found guilty of murdering Phil Nisbet.
In August last year, she was jailed for two years and eight months for sending herself death threats and pretending they were from her son Adam Kearns.
Milner became eligible for parole in June, but remained behind bars during her murder trial because the Parole Board found she remained an undue risk to the safety of the community.
The fake death threats were prompted by her son telling police and anyone who would listen that Milner had killed her second husband on May 4, 2009.
But police had ruled suicide, and it looked like she had got away with murder.
To silence her son, then aged 18, she tried to frame him early in 2010 and get him out of the picture.
She bought a cellphone and used a pre-paid SIM card to send herself the texts, claiming they were from her son, who she had taken a protection order out against.
Police arrested Mr Kearns and he spent 18 days in jail. The truth only emerged after a thorough police probe.
"Needless to say he found the experience of being remanded wrongfully in custody extremely harrowing,'' said Judge Paul Kellar, as he jailed Milner last year after she pleaded guilty to one charge of perverting the course of justice.
Judge Kellar said it was difficult to understand or speculate on her motives - but he believed the crime's intent was to adversely affect Mr Kearns' contact with his newborn son with then-girlfriend Kasey Woodstock, who he had just split from.
"That is almost too perverse to contemplate but I can't imagine what other motivation you would have had.''
The Parole Board convenor who kept Milner behind bars during her trial, Judge Raymond Kean, described the crime as unusual, calculated and "very concerning''.
In his decision, Judge Kean said her son's wrongful imprisonment had been "a very upsetting and traumatic experience'' and Milner had offered him neither an apology nor the slightest indication of guilt.
The board heard Milner had been undergoing counselling to tackle issues from her past, but no programmes to address her offending.
It said she would benefit from a group-based prison programme for female offenders but Milner had told the board she did not like participating in groups and would rather do something in the community.
The then-pending murder charge had played a part in the decision to keep Milner locked up, with Judge Kean saying it was not possible to fully assess her ongoing risk to the safety of the community.
"Unless we are satisfied she would not pose such a risk, then we cannot release her.''
Milner's sentence had been due to finish in April 2015 and she would next become eligible for parole in June next year.
Milner had earlier served home detention for five months starting in October 2010.
She had stolen $29,000 while working as an office administrator at Christchurch grounds maintenance firm, GSL, where workmates dubbed her the Black Widow because of all the references she made to "get rid'' of Mr Nisbet.
- By Kurt Bayer and Matthew Backhouse of APNZ
