Cho (Pakuranga) leads the field by eight shots after two of the scheduled three rounds at Chisholm Park.
The outstanding 15-year-old held a three-shot lead after the opening round and added a 1-under-par 71 yesterday to stay well clear of the chasing pack on even-par 144.
Cho, already a two-time New Zealand amateur champion and runner-up in the Australian amateur, had one birdie and 17 pars on the links course yesterday.
The shot she picked up was on the testing par-3 seventh.
Cho will lead New Zealand in the world amateur teams championship for the Espirito Santo Trophy later in the year.
Two older golfers are tied for second on 152 at Chisholm Park.
Waikato senior representative Chantelle Cassidy (Tokoroa) fired a second consecutive 76 yesterday, and Mun Chin Keh (Pakuranga) added a 75 to her first-round 77.
Rica Pui-Man Tse (Muriwai) is five shots further back, followed by Brittany Dryland (Maungakiekie) on 158 and Wellington senior representative Julianne Alvarez (Manor Park) on 159.
With a second round of two-under-par 69, Simon Brownlee (Muriwai) remains at the top of the leader board going into the final round of the men's under-19 championships at Balmacewen this morning.
Brownlee is 5-under on 137 and holds a four-shot lead over Owen Burgess (Russley) and Jordan Bakermans (Christchurch), while Duncan Croudis (Otago) and Bradley Kendall (Mt Maunganui) are one shot back on par.
In calmer conditions yesterday morning, Brownlee looked to lose the initiative on the front nine, turning one over, but finished strongly with birdies at 14, 16 and 17.
Burgess was consistent, adding a 70 to Wednesday's 71, while Bakermans romped up the leader board with his 69.
In sharp contrast to two sub par rounds on Wednesday, eight players broke par yesterday.
There were six in the morning but only two when the wind got up in the afternoon.
The best round of the day and the lowest score to date was posted by Tom Cardno (Waitemata) with a 4-under par 67.
Cardno had a faultless round with 14 pars and three birdies to catapult him into sixth place after two rounds.
Along with last year's under-15 winner Ryan Chisnall (Greenacres, Nelson), Cardno is on 143 with a slim chance of making up the deficit.
Croudis had an excellent chance of taking the second-round lead when he started with three birdies and had six birdies in total.
But his round was like a roller coaster and an unattractive double bogey 5 on the 12th along with a rampant hook from the next tee cost him shots.
Of the Otago golfers, Chase Thomas (Ardleigh) has played above himself, shooting two rounds of 72 to place him in the third-last group in today's showdown.
