"You thought doing what you were doing would enable him to be at home with you, and you were prepared to lie to the police to do that."

Thom was given the chance to review her police statement and confirmed its truth and accuracy.

However, her dishonesty unravelled when police intercepted a call between her and her boyfriend while he was on remand at Otago Corrections Facility on September 4.

Thom told him about the false alibi.

"What am I meant to do, though ... I've said you weren't even there."

When approached about her lies, she attempted to backtrack, telling police she must have confused the weekend in question with another.

"She stated that as police had sufficient evidence against her partner her statement should have been ignored," a summary of facts said.

She later pleaded guilty to attempting to pervert the course of justice.

Judge Phillips said they were clear attempts to minimise her criminal conduct.

Counsel Jim Takas argued Thom was four months pregnant at the time and "under quite a bit of pressure".

She had since given birth and had two other children under 6, the court heard.

Takas said a sentence of community detention would suffice but Judge Phillips was unequivocal - "[that] does not cut the mustard".

Thom, he said, was looking squarely at a stint in Christchurch Women's Prison and her children going into care.

"That would be a bit of a disaster," her counsel said.

What saved her, Judge Phillips said, was her support in the community. He sentenced her to three months' home detention and 100 hours' community work.

Her partner remains in custody and will appear in court again next month.