Jessie Waterhouse compiled a 2-1-1 score-card over her three races, giving her a massive 21-point win over her 23-year-old sister Casey Waterhouse - who finished 1-8-3 in her three outings.
Elwin suffered a crash in race one, to finish 12th in that race, and, unfortunately for her, Elwin's two impressive runner-up finishes that followed were not enough to make up for that disaster.
"It was an awesome day's racing," said Jessie Waterhouse afterwards.
"It was so good to see so many women racing and so many of them were very quick too," she said.
"I have not done much racing lately because I've been busy training as a nurse and then working fulltime. But I have a job now that allows me a bit of time to go riding.
"It has been the same for Casey too. She's been training as a child carer.
"I knew it would be hard for me with the 125cc bike up against the 250cc bike riders but I love my YZ125. I nearly got the holeshots," she smiled.
And that didn't matter, because she was in front when it mattered, at the chequered flag.
Other class winners at Summercross were Mount Maunganui's Cody Cooper (MX1 class); Hamilton's Josiah Natzke (MX2 class); Cambridge's Trent Collins (junior 12-17 years 250cc class and Youth MX class); Motueka's Josh Coppins (veterans 35-44 years); Hamilton's Darryll King (veterans over-45 years); Taupo's Wyatt Chase (junior 16-17 years 125cc); Mangakino's Maximus Purvis (junior 12-15 years 125cc); Okato's Zak Hetherington (junior 14-16 years 85cc); Matamata's Brodie Connolly (junior 12-13 years 85cc); Tauranga's Madoc Dixon (junior 8-11 years 85cc); Hamilton's Nick Westgate (pro 65cc class).