Three generations of women in a Gisborne family turned on a 12-year-old relative who claimed she had been sexually assaulted by her uncle, in a case that a judge said "made a mockery of notions of whanau".

The case involved a mother and daughter forcing the girl to retract claims that her uncle had indecently assaulted her, after a jury had found him guilty.

The women, aged 48 and 29, and both closely related to the offender, have been jailed for three years for attempting to pervert the course of justice. They cannot be named, to protect the girl.

When sentencing the pair in Gisborne District Court on July 16, Judge Tony Adeane said the girl was the subject of "a cruel course of ostracism by three generations of female relatives – grandmother, aunt and cousin".

He said the girl's parents had turned on her, "or at least stood by and failed to support her", and she was now "effectively deprived of the female side of her family".

"This girl was abandoned by people whose duty it was to support her as a victim of familial sexual abuse. In doing so, they made a mockery of the notions of whanau."

In mid-2013, while the offender was in custody pending sentencing, the two women made repeated visits to the girl's home, where they would take her aside from her parents and tell her "what her responsibilities were", the judge said.

They marched the girl to Gisborne District Court where, in front of a registrar, she signed a sworn retraction of her allegations.

Judge Adeane said the language used in the retraction was certainly not the girl's and, when she was spoken to privately by an independent lawyer, she reaffirmed her allegations against her uncle.

Throughout this time, the women were regularly phoning the offender in prison. The judge said these calls, which were intercepted, displayed the "energy and urgency" the women were putting in to persuade the girl to retract her allegations.

The women told the man they would assault the girl after the affidavit had been signed, and would get her to sign it "even if we have to kill the little beggar".

Another relative, concerned at the pair's actions, contacted police.

Judge Adeane said the women, who had no previous convictions, continued to believe the girl's allegations were false and that therefore their conduct was acceptable.

The attitudes displayed by the women during their trial, and that of the girl's grandmother, who gave evidence for the uncle, made it clear that the breakdown of family responsibilities towards the girl were beyond repair, he said.

"That is a dreadful part of the impact on her as a victim of your offending. She has suffered permanent damage and no small part of it is that she is now effectively deprived of the female side of her family."

He said there was a hardening of attitudes towards attempts to pervert the course of justice, "particularly in some communities where close-knit groups often use improper influence to attempt to alter the outcome of trials".

The uncle was sentenced to two years and three months' jail in July 2013, after a jury found him guilty of indecently assaulting the girl when she was aged 10-11. He was sentenced to a further year in jail for his part in attempting to pervert the course of justice.