Field (30), who was convicted for being an accessory to the murder of Kaitangata teenager Michael Hutchings, was sentenced to two years' imprisonment last October.
But because she had been in custody since her arrest in mid-January 2008 and served half of her two-year sentence in custody, she was eligible for release.
It is understood she could walk free as early as today, but the Department of Corrections yesterday said it did not comment on the release date of prisoners or where they were being held.
The department did confirm Field had no special conditions imposed on her, apart from the routine requirements all prisoners serving between one and two years must follow.
That has outraged Mr Hutchings' sister, Sarah (17), who described it as a devastating blow by the justice system.
Yesterday, she found support from Sensible Sentencing Trust chairman Garth McVicar, who said this was the kind of "big con" which had fooled many victims of crime into thinking those responsible would serve the full sentence imposed by judges.
"The two-year sentence was never ever going to mean that, because anybody who gets a two-year sentence is entitled to be released at half of that," he said.
Any prisoner sentenced to less than two years has their release handled by the Department of Corrections and not the Parole Board.
That means that the Hutchings family did not have to be informed about Field's release.
Nevertheless, Mr McVicar said the public had been conned and deceived by this piece of legislation.
The trust was continuing to push for a law change which meant the sentence handed out by a judge was the actual sentence served by the criminal.
In the case of Field, this would have meant she would not have been released until this time next year.
Sarah Hutchings contacted Mr McVicar on Monday night to express her concerns with the system and he said he had great sympathy for her and the situation in which lawmakers had placed her.
The public expected, and he said had every right, to believe that criminals like Field, sentenced to two years' imprisonment, should actually spend that much time behind bars.
But Mr McVicar believed a "big mindshift" towards this kind of approach was imminent, as new laws forced recidivist offenders to serve their "judge-given sentences".
In the meantime, though, he said the existing "crazy system" continued to torment victims like Miss Hutchings.
In a statement issued to the Otago Daily Times, a department spokesman said Field would be required to comply with the standard conditions laid down for all offenders sentenced to between 12 and 24 months.
These include having to regularly report to a probation officer, and restrictions on where she can live, work and with whom she can associate.
No further details were provided.
The department confirmed the sentencing judge last October set no special conditions for Field upon her release.
