A tourist who became obsessed with one of her employers during a working holiday has successfully overturned her sentence and conviction for criminal harassment.

Sin Tan Chang, 31, a Chinese national, was sentenced by Judge Brandt Shortland to nine months of intensive supervision after pleading guilty to three charges of harassment.

On appeal to the High Court, Justice Timothy Brewer said Judge Shortland was wrong not to grant Chang's application for a discharge without conviction and had not given enough weight to her mental ill-health at the time of the offending, which he said had been brought on by a sand-duning accident in Northland about eight months into her working holiday.

Chang came to New Zealand from Hong Kong in January, 2020, on a visa that entitled her to work for three months at a time.

She worked for the complainant in Northland for about three months soon after arriving in the country.

Chang did not act on her obsession but kept in touch with the woman after moving on from the job.

In September that year, Chang suffered a head injury while sand-duning and was hospitalised.

By February, last year concerns about her mental health and her behaviour towards her former employer prompted a notice trespassing her from the woman's workplace and an order to stop the harassment. But neither was effective.

Police laid two charges the following month after Chang left 25 messages on the woman's phone telling her she wanted to be in a relationship.

A further charge was laid in September after Chang turned up at the woman's house. The woman was out but her partner arrived home to find Chang on the doorstep. He told Chang to leave but she refused, acted oddly, and was consoled by a kindly neighbour until police arrived.

In sentencing Chang, Judge Shortland referred to the 2011 murder of Christie Marceau by a besotted male friend who was out on bail despite opposition from police and the victim.

That case resulted in a heightened need to assess the balance of the risk of harm against justice, Judge Shortland said. It was at the forefront of his mind in dealing with Chang. He noted Chang still had an ongoing obsession or focus on her former employer.

Justice Timothy Brewer has overturned a conviction and sentence of intensive supervision imposed on a tourist who harrassed her employer while here on a working holiday. Photo / NZME

Quashing the conviction, Justice Brewer said Chang's condition had improved considerably by sentencing - she had been on remand in custody either in prison or at the Regional Forensic Psychiatry Services Mason Clinic for five months and was ready to be released into the community. She was not identified as posing any real risk.

If discharged without conviction, she would still have been subject to compulsory treatment under the Mental Health (Compulsory Assessment and Treatment) Act.

In his view, Judge Shortland did not need to impose the more supervisory regime available on conviction, Brewer said.

While the offending was moderately serious, Chang's personal circumstances reduced the gravity of it.

Were it not for Chang's ill-health, the offending would not have occurred, Justice Brewer said.

She had no previous convictions and should have been given credit for that previous good character. There should also have been "considerable recognition" for the likely effect on her mental health of the head injury.

Convictions would deprive Chang of her good character. That was usually of little weight where there was deliberate offending, but not where the offending was due to mental ill-health.

Her chances of successfully applying to return to New Zealand would be affected by convictions and they could also affect her ability to travel to other countries, Justice Brewer said.

Even if a conviction was justified, the sentence imposed was manifestly excessive, he said.

Intensive supervision ranks immediately below home detention in the sentencing hierarchy and places significant constraints on a person's liberty. It was not imposed as the least restrictive response but as a measure to manage the risk of Chang relapsing and re-offending, which was wrong, the High Court said.

Chang was served with a notice of liability for deportation two days after arriving at the Mason Clinic but left the country voluntarily.

- Sarah Curtis, Open Justice