Miss Whitehead, of Gore, and cousin Hannah McColl, of Taranaki, shore 1283 lambs, eclipsing the previous record by 380.
Marg Baynes and her daughter Ingrid Smith had held the record of 903 since 2009, when Mrs Baynes did 433 and daughter did 470.
Miss Whitehead, who shore 686 lambs yesterday, also broke the previous solo record of 601, set by King Country-based Sacha Bond in Northern Southland last February.
The record attempt was "awesome" and went better than she expected, Miss Whitehead said.
"My secret goal was 1200.

Four years ago, Miss Whitehead was part of a four-woman team attempting to break a world shearing record and Miss McColl was her water girl.
From then on, the pair decided it would be good to attempt a world record together, Miss Whitehead said.
This was the third time she had set a world shearing record and she enjoyed the challenge.
"It’s a thrill. It’s painful but it’s fun."
Miss McColl said even though the day had its ups and downs, it was "amazing".
"It’s a dream come true doing a record with Megan."

"They’ve got the same grit and determination that she had."
Miss Whitehead’s mother, Tina McColl, and her father, Quentin Whitehead, have also been shearers.
Ms McColl said shearing ran in her family.
"It’s just come down through the McColl breed.
"They’re tough little critters."
By Sandy Eggleston