Courtney wins world title
The 18-year-old was without peer as she finished four minutes ahead of her nearest Under-19 rival and even beat all but one of the Under-24 age group competitors at the World Triathlon Championships in Vancouver last week.
Although originally trained as a middle distance runner, Gilfillan excelled in the swim leg as others had to be winched out of the 10.9 degree waters by helicopters.
"It was incredibly freezing and it got very rough," she said upon return to the Northern Rivers this week.
"I dealt with it pretty well and I led out of the swim actually.
"I couldn't feel my hands or feet the whole way and getting my wetsuit off in transition was very hard when you can't feel your hands.
"The swim is not my strongest leg but I've worked very hard on it the last few months and I'm very happy I had a good swim."
Gilfillan, who was struck with a cold a week before the race, had a 10 second lead out of the water which she maintained during the bike leg before powering home in the run.
"I got very sick a week out from my race ... and came good a couple of days before," she said.
"I just said to myself: 'I'm strong enough and I'm racing.
"That's why you train I guess.
"As long as you're safe to race it just becomes a mental battle."
Although delighted with being a World Champion, Gilfillan said she was more impressed with her showing among the older competitors.
"We started on the same leg as the 20-24 years age group. I actually led them out of the water and finished second overall for them as well," she said.
"There were about 70 older girls. We weren't racing them for medals but we did the whole race with them and to only have one of them in front of me, I was very impressed with that.
"To match it with the older girls gives me confidence to step up next year and go for higher things."
Gilfillan said she would not let her success interfere with her focus and training for future events.
"When I was at the airport I sort of started to think, what if I hadn't achieved this? What would I be feeling now?" she said.
"Either way I'm determined to get back in and train harder.
"It's a great, great feeling, but you can't let it get to you too much.
"You have to enjoy the moment with your family and then get back into training with that under your belt. It makes you hungry and it's a great feeling to train on with that."
Gilfillan will now start preparing for the Australian Under-23 elite team qualifications which start at the end of the year.
"This is all so new to me," she said.
"I only started training seriously in the last 6 months with a swim and bike coach.
"I'm going to trial for the Under-23 elite team - if I make that, that's getting pretty serious.
"Next year's world's (championships) are on Gold Coast in September which I'm excited about but it's a big journey. It's going to be a big ask."
Mum Karen was to also represent Australia in a senior division at the World Championships, but was wiped out by the same illness that affected Courtney.