When placed under pressure the New Zealand side committed some fairly soft turnovers, with their option-taking around the attacking third particularly suspect.
Southby said after showing strong improvement at training in the tight two-day turnaround between tests, she was disappointed to see the Ferns attacking game once again fall apart in Christchurch.
"I think at times we got a bit narrow in our vision, didn't quite watch what else was happening or see the best option at the time," she said.
"You've got to be able to do your own job under pressure first and foremost and I think at times we were a little bit guilty of not doing what we needed to do for the other people around us when we had the ball."
Southby's side had a dream start to the match, as the Diamonds handed them a four-goal headstart after a flurry of unforced errors - including turnovers off their first two possessions. The Ferns showed good patience to break up the suffocating Australian defence and convert their early opportunities, but their composure deserted them as the quarter wore on.
Trailing 14-11 at the first break, the Ferns were well and truly in chase mode by mid-way through the second quarter as Australia pounced on a couple of miscommunications on attack from the homeside to stretch their lead out to seven goals. After working hard to get themselves back into the contest and restore the three-goal margin at halftime, the New Zealand side again dropped the ball early in the third quarter, leaving Southby to rue the costly lapses.
"It's a big concern, we don't want to be in those positions, we want to be on the other side of the scoreboard and we had opportunities to do that, but at critical moments we didn't do what we needed to," she said.
New Zealand vice-captain Maria Tutaia believes much of her side's attacking struggles come down to poor communication.
Tutaia returned strong shooting stats in Christchurch, netting 26 of her 29 attempts, but her work around the court was not as sharp, with the veteran displaying some poor execution with her passing.
"We weren't as consistent as we would have liked. I think in terms of connections and communication it wasn't as sharp as it has been the last few trainings, so that was really disappointing," she said.
"I guess we're still a young side - some of us are talkers, some of us aren't so much - and it's about having the confidence to contribute and speak up when you need to."
Some of the toughest talking in the Ferns' camp post-loss came from one of the rookies in the group, energetic midcourter Sam Sinclair, who produced some stand-out work on defence.
"We haven't put ourselves in a very good position," she said of her side's prospects for the rest of the series.
"I hate losing - I hate it with a passion. We've got to take a good look at what we're doing, make some changes and come out firing."
The Ferns have limited time to address the issues ahead of Wednesday night's third test in Adelaide, before the series wraps up in Sydney on Saturday.
