Greene (16), a pupil at St Hilda's Collegiate, originally planned not to compete at the championships and concentrate on other international events instead.
Greene is the only Otago member of the largest New Zealand team to compete at a world junior track and field championships.
There are 23 athletes in the New Zealand team.
She will compete in the 1500m and 3000m at Moncton, Canada, in July.
Greene said she will compete in Canada instead of the Youth Olympics at Singapore a month later.
"The team management spoke to Mum and Dad at Christchurch and told them that the world championships was the better event to go to," Greene said.
There will be intense competition for Greene in Canada because she will be competing against girls two years older than herself.
"I'm pleased about that," Greene said.
"It gives me the competition I need. It will be good."
There will be a lot of international travel for Greene this year.
It started last month when she won the 3000m and was runner-up in the 1000m at the Oceania under-18 championships in Sydney.
Greene leaves Dunedin on Monday to compete at the world secondary schools cross-country championships in Slovakia on April 21.
But the biggest prize comes in July when she heads to the world junior athletics championships in Canada.
Greene reached the A category standard in the transtasman test in Auckland when she finished runner up to Canterbury's Hannah Newbould (18) in the 1500m.
Newbould won in 4min 21.73sec, while Greene clocked 4min 21.98sec.
Both runners recorded personal best times.
It was an Otago senior women's record and beat the time that Gail Metzger (Hill City) ran in 1986.
Greene was just 0.8sec outside Sue Bruce's 1981 national women's aged 16 record.
Greene is ranked sixth on the New Zealand senior women's ranking list this season with both her 1500m and 3000m times.
Her best 3000m is 9min 30.69sec.
Greene used to be coached by Dunedin's Jim Baird but earlier this year joined the squad of Maria Hassan, of Christchurch, the Athletics New Zealand national event coach for middle distance.
Her training has changed slightly and she is now running more mileage.
Her long run of the week has increased from an hour to 1hr 20min.
Two Southland athletes are also in the team. Glen Ballam will compete in the 800m and Matthew Robinson in the 4x400m relay. They are both students at the University of Otago.
