The 20-year-old Auckland student from the Pukekohe swimming club was joined on the podium by Ukraine's Kateryna Denysenko in second and America's Jessica Long took the bronze medal.
Neiufi won silver in the event at Rio Paralympics in 2016 and also silver at the world champs in London two years ago.
Neiufi displayed plenty of emotion in her win.
"As soon as I touched the wall, I'm not going to lie - I was a bit confused," she said.
