Bourne-based Constance Copestake and her own mare Aprobanta led the way on a dressage score of 38.10 to win the Racesafe National Under-18 Championship at Brand Hall in Staffordshire.
Four faults in the show jumping were not enough to knock her off the top spot after a faultless cross-country round resulting in a final score of 42.10.
Constance and her chestnut mare kept a narrow 0.70 margin ahead of second-placed Sam Ecroyd and Wodan IV, who also gained four faults in their show jumping round to finish on 42.80.
The 17-year-old is currently studying for her A-level exams and is completing an Advanced Apprenticeship in Sporting Excellence (AASE) at Hartpury College.
She said: “I’m still in shock. I didn’t know what to expect because this was Aprobanta’s first three-day event and I didn’t know how she would be on the last day.”
The nine-year-old KWPN mare by Karandasj has had a stellar career to date, netting two CIC one star wins with Copestake at Chatsworth and Aldon and winning a silver medal with Rosalind Canter at the 2011 FEI World Eventing Championships for Young Horses as a six-year-old.
Copestake is from a non-horsey family and was hooked on horse riding after a friend’s fourth birthday party at her local riding school.
The teenager is now concentrating on finishing her exams and will take a year out with the intention of focusing on horses.
She added: “The long-term view is to go to the top level. This year my plans depend on whether I am long-listed for the junior team. Plan B is to move up to two-star level with Aprobanta.”