Australia made the perfect start to the final, with Tiana Penitani crossing after 90 seconds. But New Zealand replied immediately, with Player of the Tournament Raecene McGregor stepping through for a crucial bonus-zone try. A Brigginshaw offload set up Kezie Apps, giving Australia an 8-7 halftime lead.
The teams traded tries in the second half, with Jules Newman crossing after the Ferns swept 90 metres down field, before Maynard's crucial touchdown.
It was a sweet triumph for the Ferns, especially inspirational skipper Honey Hireme, after the recent passing of her mother.
The New Zealand men couldn't back up that triumph, though they were perhaps unfortunate in a 24-10 defeat to Australia.
The hosts led 13-10 at halftime but the second period turned on a controversial try to Kyle Feldt, awarded despite the Cowboys winger seeming to ground the ball short.
That was the critical moment, before Mitchell Moses completed his hat-trick with 30 seconds to play.
The Kiwis had earlier made a strong start, with wing Reimis Smith crossing after two minutes.
Australia replied with a bonus-zone try, after a dubious one-on-one strip, as Moses cut through the heart of the defence. A Jamayne Isaako try restored the New Zealand advantage, before Moses again used his speed to give Australia a 13-10 halftime lead.
