As national women’s light-flyweight champion, the Newmarket fighter was regarded as one of the favourites to triumph in what is Europe’s biggest amateur boxing event.
Despite that pressure, Resztan went on to live up to that billing at Alexandra Palace to continue her ascent within the sport.
However, even with previous triumphs in mind, O’Reilly is just now seeing the 19-year-old put full faith in her ability.
“Demie-Jade is incredibly talented, but it is only now that she is starting to really believe that,” he said.
“A lot of boxers are like that because throughout their career they take massive steps.
“The jump up is in miles, not inches and that is a daunting prospect for anyone.
“To cope with that you have to live the sport and to her credit, she does that.
“She is a different person to a year ago and that is now starting to show itself in the performances.
“It has been about maturing in the ring. Demie-Jade belongs at this level and now she realises that.”
In order to clinch glory, the southpaw had to see off the challenge from Watford-based Rebecca Stone.
Resztan was dominant from the start and ended up advancing through to the final courtesy of a fourth-round stoppage.
That victory set up a title clash against Boston’s Adrianna Finch, who has sparred with Resztan on numerous occasions.
A close fight ensued, but it was the New Astley member that eventually came out on top.
“The girl from Watford was not a bad fighter, it was just that Demie-Jade was too experienced and too strong,” added O’Reilly.
“We know Adrianna well and she is a good girl that has boxed to a decent standard for England.
“It was an extremely tight contest and both of them gave everything they had to get the victory.
“Ultimately, Demie-Jade was just too good and deservedly won the bout.
“She is a driven winner and has shown that.”
After competing for England early next month, Resztan is planning to take a short break before she potentially begins preparations for the European Championships later this year.