It will involve interviews with "every single person involved" in the campaign including athletes, management and staff, and will be conducted by a mixed panel of independent experts and representatives from Netball NZ and High Performance Sport.
Wyllie's announcement comes after high profile netball personalities - including former assistant coach Robyn Broughton and former player Margaret Foster - on Monday slammed the coaching staff for the team's poor performances.
When asked if Southby's position was under threat, Wyllie insisted "no one person" can be blamed for the demise.
"We will leave no stone unturned in the review. Without pre-empting the findings, we do not believe responsibility rests on any one person, or event. There are usually a range of factors in sport as to why a team isn't performing at the expected level," she said.
"I think the review is first and foremost the biggest tool that we can use in working out what things didn't work and where we need to go to from here. And I think we need to let that run its course before we make any decisions."
Under Southby's leadership, the Ferns have produced some of their worst results, losing 19 from 39 matches.
Another issue that could arise during the review process is Southby's initial appointment in 2015, which has been questioned by commentators and fans, with many arguing that other more qualified candidates were overlooked.
Former Silver Ferns assistant coach and player Noeline Taurua is believed to be one of those snubbed - and has been championed as the best replacement for Southby.
While Netball NZ admitted to talking to Taurua as recently as October, Wyllie insisted Southby was the best person for the job at the time - and no decision on her future will be made until after the review.
The conversation between Netball NZ and Taurua was around coaching in New Zealand and how to bring through talented players, and coaches, Wyllie said.
She also dismissed suggestions star player Maria Folau's public support of husband Israel's controversial comments about homo-sexuality proved a distraction.
"We take our responsibility as role models for young New Zealanders very seriously," Wyllie said. "Maria chose to demonstrate her support for her husband and his beliefs and this is not a matter for Netball New Zealand to comment on."