Natasha Beth Darcy to be sentenced in Tamworth court for offering cash for lies at her trial for the murder of Walcha's Mathew Dunbar in 2017

Natasha Beth Darcy, 47, made headlines as the Widow of Walcha last year after a jury convicted her of sedating and gassing her sheep grazier partner, Mathew Dunbar, to death at his Pandora property in 2017.

Darcy is serving a 40-year sentence for murder and dialled into Tamworth Local Court from jail on Wednesday to plead guilty to acting with intent to pervert the course of justice, a charge linked to her trial.

A second count was dropped by prosecutors.

A Tamworth detective laid the charge against Darcy in the weeks after her 10-week trial wrapped up in the NSW Supreme Court in Sydney.

Darcy had put pen to paper, sending a letter from prison offering another woman $20,000 to fabricate evidence at what was then her upcoming murder trial.

"Your Honour there's a plea of guilty ... there are agreed facts on file," defence solicitor Tracey Randall told the court.

Darcy's criminal history was handed up to magistrate Julie Soars but she immediately picked up on a gaping hole.

She said it was too old to have Darcy's most serious offence listed.

"That she was convicted of murder," Ms Soars said.

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The solicitor from the state prosecuting authority, the DPP, confirmed he would provide an updated history to the court.

Ms Soars committed Darcy to the district court to front sentencing, and adjourned the matter for its first mention in the higher court in Tamworth in August.

She noted Darcy was already serving "one of the most substantial sentences handed down in recent history in NSW".

There was no application for bail.

Darcy sat silently during the committal.

"Thank you," she told the court at the end of the proceedings.

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