Prime Minister John Key is standing by the Cabinet's appointment of Christine Rankin to the Families Commission but has effectively put her on notice to stick to the issues of families and child abuse - not her private life.

"That's what I want to hear her talking about and nothing else," Mr Key said at his post-Cabinet press conference yesterday.

It is understood the Government has been shocked by the fallout over her appointment which, instead of dying down, intensified after murky details of her private life became public at the weekend.

The Cabinet's delay yesterday in finalising the appointment of the Transition Agency to oversee the Auckland Super City is understood to be a consequence of the debacle.

The Government has decided to take more time over its appointments where there may be potential fish-hooks.

The role that Social Development Minister Paula Bennett played in strongly promoting Ms Rankin is also coming under scrutiny.

Sunday newspapers revealed that Ms Rankin married her fourth husband, Kim MacIntyre, about three months after his previous wife, Wellington real estate agent Margo McAuley, committed suicide.

Ms Rankin went on TVNZ's Sunday show that night to deny claims that she was having an affair with Mr MacIntyre at the time of his wife's death.

Asked if she could keep her job as a families commissioner, Mr Key said: "Providing she stays focused on that issue, providing she continues to be a strong advocate in that area I believe she can."

Mr Key would not criticise Ms Rankin for having gone public, saying the media had made serious allegations "against her character".

"She probably needed the position to put her side of the story," he said. "But as far as I am concerned she has been appointed as a commissioner, one of seven in a part-time job, to advocate for families and - particularly because of her expertise when it comes to abused children - that's what I want to hear her talking about and nothing else."

Ms Rankin is said to be close to Paula Bennett and has become something of a mentor to her, both during the campaign for her successful election as MP for Waitakere last year and in helping her to adjust as minister for the department Ms Rankin once ran.

Both overcame the struggles of sole parenthood to land high-ranking posts.

Paula Bennett is said to have strongly supported Ms Rankin's appointment against the opposition of some colleagues thought to have included Justice Minister Simon Power.

The Cabinet approved the appointment on Monday, May 4, and it was announced on Tuesday, May 12.

Mr Key said yesterday that his own staff had told him of rumours surrounding Ms Rankin's private life on the day of the announcement.

He said Paula Bennett had learned of them about a week before but checked them out with Ms Rankin and that Ms Rankin had totally refuted them.

He was not concerned that Paula Bennett had not informed him earlier and accepted that she had done "due diligence".

"There's always a lot of rumours flying around Parliament and I accept that she satisfied herself that there was no basis to them."

Ms Rankin gained political notoriety in 1999 when Labour in Opposition vilified her for what it called her "culture of extravagance" as head of Work and Income.

In recent years she has become politically active opposing the anti-smacking law, joining National and getting elected to the Auckland Regional Council.