Chasing 347, Kerr hit a six and 23 fours from 139 balls as her team surpassed India's feat of overhauling Australia's total of 338 at last year's World Cup.
It was the second-highest score of Kerr's ODI career, behind her 232 not out against Ireland in 2018.
"It's number one," Kerr said. "To get a big hundred like that in a big chase against a quality side is definitely number one."
"I was really calm out there and just was so focused on, simplifying it to each over and where we needed to be to get the job done," she told reporters.
"When I did hit the winning runs, I was actually pretty fizzed. It shows how much it means to me. I'm a pretty relaxed character with celebrations and all that stuff. But that was special."
The 25-year-old guided New Zealand to a series-levelling victory with two balls to spare, and the teams meet again in the deciding match on Saturday.