Making her international debut meant Allen, of Ashbourne, missed out on collecting the Girls' Player of the Year title at this year's Derbyshire Tennis awards.
But Barnes – who is also talent performance manager for the Midlands – said she will have gained a lot of confidence from her performance at the tennis centre in Antwerp.
He said: "At Victoria's age, you are starting to take tennis more seriously.
"And if you are planning to have a successful international career, it's important to be thinking about milestones like this.
"The nice thing about this event was that it was two days long and just a short journey on the Eurostar – not a big trip over to America, which can be very time-consuming.
"You get the benefits of going abroad and testing yourself out against other players without too much fuss. It's absolutely critical.
"And given how well Victoria performed on her first time away, it can only motivate her to keep pushing on.
"That's why this is a massive step forward."
For the past 12 months, Allen has been training at the MyTennis Academy in Loughborough and has maintained the number one ranking for her age group across the UK.
Last year, she picked up the 12-and-under singles, 12-and-under doubles and 14-and-under singles at the Derbyshire County Closed event.
Allen was part of a six-strong squad, comprising three boys and three girls, which travelled to Belgium.
The team faced competition from players from the Netherlands, a French Belgian team and a Flemish Belgian team.
Trophies up for grabs were the girls' and boys' singles and doubles.
Barnes said: "Victoria was the second girl in the team and she had a great attitude throughout the tournament.
"It's clear she's made a big improvement to her game over the past six months to a year and she took the whole international debut in her stride.
"It's never easy working with coaches who you don't spend every day with but she was very professional and mature throughout the event.
"Those attributes are a real credit to her coaches and her parents.
Barnes – a former Ripley Mill Hill pupil who has represented Derbyshire at senior county level on numerous occasions – said Allen's next priorities would be to return to training at Loughborough and work towards being selected for an international training camp in Croatia later this year.
He said: "Victoria will have certainly done herself a lot of favours with her performance in Belgium towards being picked for the camp.
"There's also a good chance her attitude will go a long way in getting her noticed for such opportunities.
"She's definitely a promising young talent for the future."