Asked how she coped with any nerves, Tweed acknowledged she was "pretty nervous" when she walked out to the mark for the run-off.
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"As soon as I started running my dog, I just did my thing and away we went," she said.
Tweed comes from Waitahuna, where her father Roger is also a successful triallist.
She started dog-trialling when she was still at school.
Listen to Jamie Mackay's interview with Stephanie Tweed on The Country in the audio below:
Grit was the offspring of Mr Tweed's own champion trial dog Gemma, a two-time South Island straight hunt champion.
In 2016, when the Tweed father-and-daughter were competing at the New Zealand championships at Omarama, Mr Tweed said that while Gemma had been his most successful dog in terms of wins, he believed her offspring could be even better.
At that time, Mr Tweed said he believed Grit was "as good as there is".
Grit, who is just over 5 and a half, had been an easy dog to train.
"He just wants to be good for you really," Tweed said.
Her father was not at the championships but was "pretty chuffed" when he heard the news.
It has been a stellar month for female triallists in what has traditionally been a male-dominated sport.
At the South Island championships at Hanmer Springs, the zig zag hunt was won by Jo Waugh, of Matawai (near Gisborne), the first woman to win an island title.
Miss Tweed was third in that event with Grit's daughter Lou. Rebecca Baynes (Wairoa) was sixth.