It's been a rapid transition.
The younger sister of Freedom Vahaakolo, the former Highlanders wing, joined the Blues for the 2023 Super Rugby Aupiki season, and after an impressive debut season with the Blues, she won a full-time Black Ferns contract.
She made her Test debut for the Black Ferns against Australia and, at season's end, was awarded World Rugby's Women's 15s Breakthrough Player of the Year. By the end of the 2024 Black Ferns' season, she had completed 13 Tests.
Now Sevens has attracted her attention.
In announcing his first squad for the season, Black Ferns Sevens coach Cory Sweeney said, "Katelyn's focus is the Rugby World Cup next year, but it's a perfect opportunity to bring her in, introduce her to the Sevens environment and, hopefully, help her 15s pre-season.
"She is a strong learner, has huge energy and wants to know as much as she can. On the field, she is strong, physical, fast, has great feet and can make a whole lot of nothing."
Vahaakolo told NZR+ it had been challenging and daunting to join the Sevens group, but the group was welcoming.
"Walking in on day one I was thinking, are they going to make me do the Bronco or something? But then, as soon as I got around the girls I just felt really comfortable."
She said being in a smaller group than a 15s environment meant the players made an effort to connect more, and that was because they had a central base. She felt that could be a helpful approach for the 15s.
There are similarities between the two teams, especially in terms of being family-driven.
"There's a real belonging in the rugby community with the Black Ferns, both 15s and Sevens."
Being part of the Sevens group would aid her in her preparation for next year's Rugby World Cup, and she believes it will make her faster, fitter, and more confident in bigger spaces.
"In my World XVs campaign, I was lacking confidence when there were big spaces, and I had to make my tackles. Being in this environment will really challenge that and expose that for me.
Even though I'm away from 15s for a little bit, it's going to make me a better player and probably a better person, too. And it's going to help me connect more with those around me."
It had always been her goal to play Black Ferns Sevens rugby, and she regrets that a player who inspired her, Portia Woodman-Wickliffe, was no longer involved. But she enjoys working with Michaela Blyde and Theresa Fitzpatrick.
"My ultimate goal is to go to the Olympics and win a gold medal for New Zealand."
Playing in the Sevens series was outside her goals for this season.
"What I'm looking forward to most in the next couple of weeks is experiencing what it's like to be in the World Series, whether I play or not. Just being in that environment, the girls have told me how busy, how exciting it is."