The 22-year-old failed to qualify for the London 2012 Olympics last summer after being hampered by glandular fever and tonsillitis but opened her campaign in Leeds with a win in the 800m freestyle on day one. It was an emphatic victory too as she set a new Welsh record and the fastest time in the world this year while on day three she won the non-Olympic 1500m freestyle by almost ten seconds.
And, on the last night of the inaugural meet in Leeds, Carlin completed a hat-trick of wins in the 400m freestyle clocking 4:07.14minutes with Hannah Miley over two seconds behind in second and Aimee Willmott third.
And Carlin, who set a Welsh record of 16:18.80 in the 1500m freestyle but was just shy of doing so in the 400m, will now sit down and decide on the perfect event for this summer's World Championships in Barcelona.
"I'm really happy with that. It was always going to be tough after the 1500m but I just said to my coach that I wanted to give it a go; to come out with gold is fantastic," said Carlin.
"The 400m is my favourite event, but my coach thinks I may be better suited to the 800m and 1500m so we'll need to have a sit down before June to discuss which to prioritise for the trials."
Joe Roebuck also completed a successful hat-trick in Leeds after winning the 200m medley in 2:00.04 adding to his earlier triumphs in the 100m and 200m butterfly events.
Roebuck competed in the 200m butterfly and 400m and 200m medleys at the London 2012 Olympics but failed to reach a single final although he admits his attentions will be mainly on the latter this summer.
"It was really tough race but I enjoyed being up against such a high-calibre field. I'm concentrating on the 200m medley and 100m and 200m butterfly at the moment rather than the 400m," said Roebuck.
"So I'm glad to have won gold in each of those events here. I enjoy the 200m more so I will be focusing on that for the rest of the season and will continue to work hard on my sprint speed in training."
James Guy was celebrating his own double winning the 800m freestyle having taken victory in the 200m freestyle on day three while Lizzie Simmonds came out on top in the 200m backstroke.
Two-time world champion Liam Tancock had to settle for second in his signature 50m backstroke as Dutch swimmer Bastiaan Lijesen took the win by less than two tenths of a second.
Olympic champion Ruta Meilutyte, based in Britain but who swims for Lithuania, was among those toasting two wins after adding victory in the 50m breaststroke to her success over double the distance.
Anthony Ervin, the Olympic 50m freestyle champion from Sydney 2000 and who won that event earlier in the week, completed his outing in Leeds with another victory.
He won the 100m freestyle in 49.21 while Jeanette Ottesen Gray, winner of the 50m butterfly in Leeds, triumphed over double the distance in a season's best time of 58.99.
© Sportsbeat 2013