The partner of a senior Mongrel Mob member says she began dealing and supplying commercial quantities of class A and B drugs after a fatal shooting at her home.

Sharon Marfell is the mother of Kahlee Marfell, who together with her then partner Robert Nelson, and Marfell's 17-year-old nephew, were shot in a violent home invasion in Hamilton in July 2018.

Nelson, 23, died from his injuries, while Marfell's nephew and daughter survived.

Four years on, no one has been arrested for the murder.

But this incident, Marfell said through her lawyer Roger Laybourn, was the reason she used, sold, and possessed methamphetamine and GBL.

The 49-year-old's claim was disputed by Crown prosecutor Jacinda Hamilton who told Justice Lang in the High Court at Hamilton today it was "far more likely" the drug dealing led to the shooting as the home invaders were allegedly there looking for Marfell's partner and co-defendant, senior Mongrel Mob member Mark Griffiths.

Marfell appeared for sentencing on Friday morning on seven charges of supplying P, and one each of conspiring to sell P, possessing P for supply, participating in an organised criminal group and possession and supply of GBL between October 2019 and November 12, 2020.

Griffiths continues to defend his charges and his case is set to go to trial.

The pair were arrested as part of Operation Oakville, a police sting netting those behind a network of class A and B drug sales in Waikato, Auckland and Wellington.

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Griffiths is allegedly the leader of the drug dealing distribution network, but police investigations found Marfell was heavily involved, travelling to get drugs and supplying them to other members of the Mongrel Mob and her own customers.

As well as selling drugs, she also played a part in collecting money from customers with a drug debt and had three others working for her.

Police at the fatal shooting scene on Matthews Cres, Melville, in July 2018. Photo / Jason Oxenham

Marfell and Griffiths were arrested on their way back from Auckland after picking up 2kg of P on November 12, 2020.

They were involved in a pursuit with police who noticed a cardboard box being thrown from the vehicle after it failed to stop.

The box was later found containing 124g of P.

A search of their home uncovered eight 1-litre bottles of GBL and two other 5-litre bottles which had GBL residue.

Covert recordings also revealed Marfell stating she could supply as much P as they wanted for $400 a gram, and that she'd sold 40ml of GBL on five separate occasions.

She also told her associates that she wouldn't sell any less than one litre of GBL at a time.

A financial analysis of her accounts revealed that between January 2017 and November 2020, they had an "unknown source of income" of $713,000.

Hamilton said as well as meth, Marfell was involved in the wholesale distribution of GBL with intercepted recordings revealing her saying she wouldn't sell any less than one litre at a time.

As for the fatal shooting, the Crown said the police investigation which began in October 2019 was already "very well established".

"This offending was motivated by a gang-entwined lifestyle and the event in 2018 in fact reflects the offending that was occurring," Hamilton told the court.

"It's acknowledged by the Crown that nobody has been arrested for that offending, but what can be said is that the perpetrators were looking for Mr Griffiths, making it clear that Mr Griffiths was the target and as we know, more often than not, that it's with this type of illegal drug dealing that leads to that type of behaviour.

"The Crown rejects the submission that they were the factor that has led her into this large-scale operation."

Robert Nelson, 23, died while his former partner Kahlee Marfell survived her shooting injuries after a violent home invasion in July 2018. Photo / Supplied

She urged Justice Lang to instead treat Marfell's drug offending in the "context of [her] long-standing involvement in the Mongrel Mob in the Waikato region".

"The group of individuals led by her were either Mongrel Mob members or close associates."

Hamilton added that the quantities recorded by police should be seen as "conservative".

Laybourn said he didn't dispute the offending was serious: "It's obvious."

He said his client didn't have an active role or involvement in the gang, rather she had been in a relationship with Griffiths for 20 years.

"That was a huge influence in her personal life and it's clear that she really had no discernible involvement until Operation Oakville came into play.

"It can't be dismissed as a coincidence that she had a very traumatic incident in 2018 and then we have the first time evidence of a more active involvement with her partner.

"It's my submission that can't be completely divorced as a reason behind it", and that at one point Marfell had her own cleaning business with "legitimate income".

Marfell was genuinely remorseful and she had not breached her electronically monitored bail during the 18 months she was on it, which allowed variations for her to travel from her Tauranga home to Rotorua for courses.

Senior Mongrel Mob member Mark Griffiths has pleaded not guilty to all of his drug charges after being arrested as a part of Operation Oakville in November 2020. Photo / Supplied

She had already begun and was doing well on rehabilitative courses for her P addiction, Laybourn said.

"Clearly had she not had a methamphetamine addiction she would not have got herself involved in this level of offending."

Justice Lang said Marfell was "very close to the source of the methamphetamine and shared in the substantial financial benefits of the operation".

While Justice Lang took a starting point for her jail term of 13 years and six months, he also had to give her discounts for her guilty plea, contents of her cultural report, and remorse totalling 45 per cent.

Marfell had suffered "an extremely troubled childhood" due to a poor relationship with her mother, which included emotional deprivation and varying forms of abuse from wider family.

She failed at school, leaving young before getting into drugs.

While the Crown took issue with her excuse for this drug offending, and her life spiraling out of control, Justice Lang accepted it would have increased significantly at that point.

Justice Lang jailed Marfell for seven years after giving her further credit for spending 18 months on e-bail without any issues.

- Belinda Feek, Open Justice