Just months after taking up the sport, the St Hilda's Collegiate pupil has claimed the girls under-19 national secondary schools triathlon title in Nelson.
The 17-year-old completed the 550m swim, 16.3km bike and 4km run in 57min 53sec.
That enabled her to edge St Andrews College's Mya Graham in an exciting finish.
Natalie Mitchell, of Mount Aspiring College, also had a strong showing in the race, finishing fifth in 59min 02sec.
Crooks was also second in the aquathlon, in which competitors completed a 2km run, 600m swim and finish with another 2km run.
Her time of 29min 14sec meant she was comfortably second although she trailed Baradene's Isabella Morton.
It was a big result for the year 13 pupil so soon after making the transition to the sport.
She has previously excelled in swimming, having won national medals and represented New Zealand.
She had also had success in running, which she had done on the side until recently.
Mount Aspiring College's Gregor Findlay finished third in the boys aquathlon.
