A UMR poll obtained by the Herald showed the Green vote had fallen from 15 per cent to 8 per cent.
Just 24 hours before her resignation, Turei had said she would remain as co-leader no matter what the polls showed. But speaking at a press conference yesterday, said she changed her mind while in a taxi between meetings in Wellington.
Smiling occasionally and appeared relieved at times, she said her main reason for quitting was the extreme scrutiny of her family since she admitted to historical benefit fraud three weeks ago.
She had expected some level of inquiry, but "not to that degree", she said.
The ongoing controversy had hindered her party's bid to enter Government for the first time in its history, she said.
Co-leader James Shaw will lead the party alone until Turei's replacement is chosen next year. Julie-Anne Genter, Marama Davidson and Chloe Swarbrick will be among the frontrunners to replace her.
Just before her resignation, Radio NZ had reported that a close friend of Turei's had strongly questioned her personal story, saying that she had been well supported by her daughter's grandparents and had not been in poverty in her 20s.
Turei insisted that it was neither this latest allegation nor the polls that influenced her resignation.
Shaw admitted that Turei's admission about her past had made party members and MPs uncomfortable, but they had felt it had started an important debate about welfare.
"We have paid a heavy price for that, and Metiria has paid a particularly heavy price for that."
Labour appears to have been the biggest beneficiary of the Green Party's fall in popularity, with both its personal vote and leader Jacinda Ardern's popularity soaring in the latest poll.
Ardern paid tribute to Turei yesterday, saying she had made an "enormous" contribution to politics and important causes.
New Zealand First leader Winston Peters said Turei's admission had been compounded by "seriously bad PR and decision-making".
Former Green MP Sue Bradford, who lost to Turei in the leadership run-off in 2009, said she could understand why Turei had decided to go.
"She's obviously doing it for her family and herself and the party, and I totally feel for her on that level.
"She stood up for beneficiaries, for Maori and women trying to bring up their kids on the welfare system and she's really copped it as a result. I'm sad for her and I'm sad for this country that this is the way so many people react."