The 15-year-old Shropshire golfer, who honed her skills at Shrewsbury Golf Club, has just travelled to Iceland to take part in the European Girls’ Team Championship from July 5-9.
McDonald-O'Brien was among six girls chosen by England Golf for the under-18s contest, where 18 teams teed off at the Oddur Golf Club in Reykjavik.
The Shropshire ace won three out of her five matches, topping the bill for England, who finished fourth.
Alongside that the teenager, who attends Moreton Hall School in Oswestry, has also been selected by England Golf to play in the upcoming European Young Masters tournament in Finland.
McDonald-O'Brien will take part in the under-16s competition at Linna Golf near the city of Hameenlinna from July 18.
Her mother Alison McDonald told the Shropshire Star: "She is so excited! We hadn't really thought we'd be on the radar for the Iceland trip, but Isla was absolutely delighted.
"England Golf refer to it as their 'Olympic gold medal' and it's in a similar format to the Ryder Cup. They had a big zoom meeting before they went and they were told they could wear England ribbons and flags and Isla was so excited for it.
"She's been picked for both tournaments because she's had such a good season. It's been a nice surprise for all her hard work – she's had a great run of tournaments.
"I'm just excited for the opportunities she is getting and the exposure to play internationally with the top girls in Europe will be a really good challenge for her to be a part of. She should be very proud."
This latest achievement comes after the young golfer secured a highly-impressive shared runners-up spot in The R&A Girls’ Under-16 Amateur Championship in April at Enville Golf Club in Stourbridge.
The youngster – who has been playing golf since the age of five – has impressive pedigree on the international circuit, having previously represented her country at under-16 level.
Although no team announcement has been made yet, McDonald-O'Brien is also in contention to be selected for the Great Britain and Ireland squad to face a European team in the Junior Vagliano Trophy. This year's event is being held in Blairgowrie, Scotland on August 26 and 27.