Aplin's scores, combined with top placings from her team members, contributed to the Hawke's Bay team's third place, their best in 15 years.
Fellow junior Tess Gordon, riding Aatahua Captivate, and senior Dannevirke rider Willa Aitken, on Kirkwood Greenlight, were alsoprominent.
Other team members, Sarah Marett on Tui's Minstrel, who won the Level 3 Championship, Olivia Goggin riding JK Legacy and Emma Dunderdale riding Alonzo Fanticy also scored highly in their tests.
The event, which was held over two days at the Dannevirke Showgrounds, was a special occasion. Teams from the South Island and the North Island only compete at the same venue every four years, making a genuine national competition.
Riders from Otago-Southland and Canterbury areas made the trek north for the champs.
The Canterbury team was sixth in the team competition with team member Jordan Shrimpton, riding Mister Puzzle, picking up two high placings in the championship classes.
"The venue was ideal, it made for that feeling, of a very important event, which it was," said Hazel Thomson, president of the Pony Club Manawatu-West Coast Area.
Dressage is usually an individual sport and all participants enjoyed the team aspect.
Teams were made up of three senior and three junior riders and placings were determined by the top four scores from both days.
"The consistently high results by the team meant that every score could potentially count," Hawke's Bay team coach Anna Williams said.
"Points at the top were very close with only a few percentage points between first and third."
Williams, herself a past competitor at Pony Club Dressage Championships, now rides at national level 5.
"We are lucky to have Anna as our coach," Tony Marret said.
"Competing at a high level, yet herself a young rider, she relates well to a young team."
These champs are busy for the riders, as every rider also enters supporting classes, apart from their championship ones, which include dressage in pairs, in fours as a quadrille and with little jumps included - prix caprilli.
- Final scores for the top three teams were: Franklin Thames Valley Area Pony Club 551.8 points; Taranaki Area 542.2 points; Hawke's Bay Area Pony Club 539.8 points.