Helena Vega Lozano, chairman of RDA UK, said: “It’s a huge honour for the Princess to come to the RDA as her only event since the accident.
“As soon as she got out of the car she said: ‘I can’t remember a single thing about it’.”
The Princess was concussed after apparently being kicked in the head by a horse while walking on her Gatcombe Park estate in Gloucestershire.
The exact circumstances of the June 23 accident remain unknown as the Princess was unable to recall what had happened and there were no witnesses.
She was rushed to Southmead Hospital in Bristol by ambulance and spent five nights as an in-patient before being discharged on June 28 to convalesce at home.
Royal aides said Friday’s engagement was the first step in a gradual return to full public duty in line with medical protocols for those recovering from concussion.
The Princess greeted officials from the RDA before walking inside a large indoor arena to present 23 awards to the charity’s coaches and volunteers.
There were chairs available but the Princess chose to remain standing as she spent time chatting to the award winners who stepped up to collect their certificates.
Vega Lozano added: “It’s hugely motivating and inspiring to have her here.”
The Princess has enjoyed a long association with the RDA, becoming its patron in November 1971 and president in March 1986.
One aide said her insistence on returning to work as soon as possible was typical of her no-nonsense attitude and dislike of fuss.
The Princess had always been scheduled to attend the event, the first day of a three-day competition.
But rather than a two-hour visit, which would have included a tour of the area, including an outdoor school where carriage riding was taking place, it was restricted to a visit that lasted just under one hour.
Michael Bishop, chief executive of the RDA, said: “We’re delighted that she was able to make it. Her commitment to the RDA is really welcome and well known.”
He added: “The princess was on super form. It was lovely to see her again. She was very engaged while talking with all the volunteers and participants and there were a few quips thrown in, too. She was very switched on and recognised many of the volunteers because she had met them before.”
Avril Nicholl, 83, from County Antrim, Northern Ireland, of the Ballyclare Group, accepted an award on behalf of a young autistic rider.
She said: “We were told not to ask her about it but I couldn’t let it go by without saying, ‘I’m so happy you could come’. She said ‘It is so kind of you to say that’.”
The RDA National Championship is the biggest equestrian event of its kind for disabled competitors who take part in dressage, vaulting, endurance showjumping, carriage driving, performance showing and countryside challenge classes.
British contenders for the Paris 2024 Paralympic Games, including Sophie Christiansen, Natasha Baker, Gabriella Blake, Georgia Wilson and Mari Durward-Akhurst, all started their competitive journey at the RDA national championships.