She reappeared today before Judge Denise Clark who said aggravating her situation was the fact it was carried out over a long period of time and involved a significant amount of money.
However, she took into account her previous good character as a first-time offender.
Isherwood's counsel, Rob Weir, said her early guilty plea was an indicator of the deep remorse that she felt.
"In many ways one of the hardest things that she has had to do is face up to her immediate whanau . . . she understands that she has to be punished but she also feels very heavily the breach of her whanau that has occurred, letting them down."
She was realistic about the prospect of a jail term, he said, stating it was "unavoidable".
As for her offending, he said Isherwood had simply "buried her head in the sand and not realised her obligations".
She had also sought help for her gambling addiction which she had recognised was a problem, he said.
An IRD investigation revealed Isherwood's company, Mana Scaffolding Ltd, earned $1.64 million between January 2011 and February 2016 for which no tax or PAYE had been paid.
The 46-year-old was employed with IRD's call centre for 12 months before going on parental leave in August 2002.
Her role included answering income tax, student loan and family tax queries as well as modifying and confirming income statements and personal tax summaries.
In 2008, Isherwood and her partner set up Mana Scaffolding Ltd. Income tax returns were filed for the tax years 2009 and 2010 totalling just over $36,000.
The company was eventually struck off by the Companies Register in July 2011.
However, in 2015, one of Isherwood's employees applied to IRD about Working for Families tax credits.
When the department looked into its employment history, it discovered the employee didn't have any.
Isherwood's offending added up to $603,000, however that excluded penalties and interest.
Judge Clark had a starting point of 5 years' jail but gave Isherwood a 40 per cent discount for not only her early guilty plea but also her remorse, steps towards rehabilitating herself and the large amount of support she had from family and friends who were in court today.