"This is not about playing politics. It is about the party going back to its followers and the followers directing them. I don't have to follow that line anymore and I'm not prepared to. What I'm doing is expressing a personal view point and I think [Clark] would do a good job."
She also rejected a claim by NZ First leader Winston Peters that Fox and Flavell's criticism of Clark was "treacherous" and "petty grandstanding."
"If anyone is treacherous it's himself. He constantly, deliberately votes to appeal to redneck New Zealand and he should be ashamed of himself."
Labour MP Kelvin Davis says the Maori Party not supporting Clark's bid has nothing to do with the former prime minister and is "political hysteria", .
"It's just to make a political point. This is nothing to do with Helen Clark, this is everything to do with the Maori Party trying to be relevant," said Davis, MP for Te Tai Tokerau.
The decision to not support Clark has also been condemned by former Maori Affairs Minister Dover Samuels as "payback".
Flavell told the Herald the party had good reason not to back Clark to become the world's top diplomat.
"Some people say that we should get over it and move on. Yeah, sure, and there's a willingness for our people to have a look at it again.
"But she has to show some acknowledgement that in the time that she was leading the government that she got it wrong."
Davis said reasons cited by the Maori Party for not supporting Clark didn't stack up.
Labour had admitted the Foreshore and Seabed Act was a "black mark" on its history, he said, and Clark had not signed the UN Declaration on the Rights of Indigenous Peoples because at the time it couldn't honour all of the articles.
"Marama Fox needs to explain why she is part of a Government that has signed it, but is not honouring it."
Davis said blaming Clark for being prime minister when the infamous Te Urewera raids occurred was also wrong, because politicians were unable to influence police operational matters.
Fox said yesterday that Clark should apologise to show she had learned from her "mistakes".
They included Labour not supporting the UN Declaration on the Rights of Indigenous Peoples (DRIP) and it introducing the Foreshore and Seabed Act.
In response to a Court of Appeal decision, the act removed the right of iwi to claim legal ownership of New Zealand beaches through the courts but set up a process for tribes with close connections to specific marine areas to exercise management over it.
Fox's comments provoked New Zealand First leader Winston Peters to accuse the Maori Party of being "treacherous in the extreme".
"It is petty grand standing without any principle," he said. "the reality is the Maori Party is desperately appearing to be relevant."
And former Labour minister Dover Samuels said the Maori Party had "set aside New Zealand's interest".
"It is payback time for what they see as something that Helen Clark did in terms of the Foreshore and Seabed [legislation]," Samuels told Radio New Zealand.
Whether to support Clark was a major issue for the Maori Party, Flavell said, and not one taken lightly.
"It was given a fair bit of discussion at one of our national meetings and our position was really clear, and it's not to put a dampener on the application because obviously she has some good skills.
"But until such time as there was an acknowledgement of what happened, and an apology, then we basically can't endorse her."
Clark, a former Labour Prime Minister of nine-years standing, and currently head of the UN Development Programme, is one of 12 candidates seeking the position.
She has the support of almost all the Parliament, especially the exuberant support of Prime Minister John Key, the politician who defeated her in 2008.
Relations between Labour and the tiny Maori Party have never been good.
Labour holds six of the seven Maori seats and the Maori Party holds one of them. It was founded by Dame Tariana Turia who broke away from Labour over the foreshore and seabed policy.
The Security Council will hold a second secret ballot early Saturday morning, New Zealand time. Clark finished sixth in the last ballot.
Labour leader Andrew Little said Fox's comments were disappointing.
"Every New Zealander should be behind that and I think it, frankly, stinks that the Maori Party say they are not going to support it."
Helen Clark said in a statement that New Zealand fully supported the negotiations on the UN Declaration on the Rights of Indigenous Peoples.
"We asked for more time to improve the Declaration to make it fully capable of implementation in all countries.
"At that time we were concerned that some aspects of the UNDRIP cut across New Zealand's constitutional framework and legal system.
"New Zealand was however at the forefront of implementing most of the rights in the UNDRIP.
"I was pleased to see that the Government was able to support the Declaration in 2010."