Otago defender Zoe Walker had an outstanding tournament and will join team-mates Te Paea Selby-Rickit and Stacey Peters at the trials in Auckland later this month, while rookie Steel defender Storm Purvis has also been invited to trial.
Purvis is one of five nominees for the ANZ Championships' best young player award alongside former Steel players Julianna Naoupu and Te Huinga Reo Selby-Rickit.
Purvis impressed in her debut when she helped the Steel upset the Magic in the opening game of the ANZ Championship and was a regular starter at goal keep.
All 18 players selected for the trial will be eligible for the world youth championships in Glasgow in 2013, New Zealand under-21 team coach Janine Southby said.
The New Zealand under-21 squad will be finalised at the conclusion of the national championships in October but a squad of 12 will be named at the conclusion of the trial for an under-21 tournament in Melbourne from August 20-30.