Casey Marie Chamberlain, 22, has been jailed for her role in the robbery of a drug dealer who sold rock salt as crystal meth.

Being set up for a robbery might be regarded as "an occupational hazard" for dealers who sell rock salt as crystal meth, the Christchurch District Court has heard.

The dealer had sold rock salt "to a group for whom the Disputes Tribunal is not the first or most obvious place of recourse", said Craig Ruane, defence counsel for Casey Marie Chamberlain, 22.

Chamberlain was sobbing and in tears as she heard from Judge Paul Kellar on Thursday that she was going to jail for one year and ten months for her role in the robbery of the dealer.

The case began as a kidnapping of the drug dealer, but Chamberlain pleaded guilty when the charge was reduced in March to assault with intent to rob.

Her partner at the time, Chad Adam Carrington, 25, has already been jailed for two years. A third alleged offender, who the police say was armed with a Taser, has pleaded not guilty and will go on trial.

Ruane said Chamberlain did not have an extensive criminal history and the incident "rapidly spiralled way beyond her contemplation or expectation".

He described Carrington as "a man who a parent would not consider was suitable for their daughter". He had a serious criminal history.

The group had felt "ripped off" by being sold rock salt instead of methamphetamine, and being set up for robbery might be considered an occupational hazard for dealers who sold things that were not what they said.

Judge Kellar said the dealer was contacted when her advertising was noticed on Facebook. She was lured to an Armagh St house where some of the group lived, ostensibly for another drug deal.

Once she was inside, Carrington locked the door, demanded her cellphone, and another woman allegedly threatened her with a crackling Taser held near her head. Carrington went outside and told the dealer's waiting boyfriend that they better return the $300 from the earlier drug deal if he wanted to see his girlfriend again.

The boyfriend drove off and called police.

The dealer had been punched several times, including once by Chamberlain. "Undoubtedly the experience must have been most unsettling for her," the judge said.

Chamberlain was seen as a medium risk of offending. She said she had used cannabis regularly but only used methamphetamine socially, three or four times. While on bail she breached her curfew twice, and admitted not living at the required address.

She had been living "an unstructured lifestyle". She was unemployed and was the mother of a child who was not in her care.