With the Diamonds defeated in double extra time, Muir has no doubt of Plummer's approach when they defend their world championship title in Singapore next July.
"Norma will be coming out like a wounded rhino," she said today.
To that end, Muir said, the New Zealanders might revel in their hard-fought win, but once the celebrations were over, it would be back to the drawing board.
"I'm sure we won't want to take things too lightly, and so after the celebrations it'll be straight back to the business. We've got a lot of room for improvement yet."
Muir coached New Zealand for 15 years until 1988, along the way picking up a world championship title in 1987.
The grand dame of New Zealand netball was still buzzing today from the win, but - ever the pragmatist - couldn't resist adding a note of caution.
"I think we've improved a lot with our defensive work through court - I'm not criticising it all. But at our defensive end, if it comes down too fast, it's very hard to stop," Muir said.
"There were about three plays that Australia did in that game that shot us to bits, and we've got to work on that.
"I do believe Australia have always gone for speed, and we want to make it that speed kills."
To do that, she said, New Zealand would need to cut down the error rate, and up the defensive work rate from the attacking midcourt and shooters
Ever the diplomat, Muir was reluctant to single out individual players for kudos, preferring instead to highlight the team effort.
However, she could not deny the impact of goal attack Maria Tutaia, who had her best game in the black dress with a performance which combined sublime shooting with canny court play.
"I was impressed with Maria in her step up-- sometimes her shooting's been good, but the court work hasn't quite been there.
"Last night, she looked mentally tough, and she shot the lights out of them."
Muir said it was a given that evergreen shooter Irene van Dyn would be heavily marked -- towering Australian goal keep Susan Fuhrmann shadowed her every move -- but the way Tutaia had stepped up had been superb.
"I'd single her out as having an impact... The beauty was that Maria didn't get too far away from the goal circle," Muir said.
"Irene came out a few times, but Maria stayed close and took all the long shots and Irene rebounded. That was really sensible stuff."
Another factor in the win were halftime changes made by coaches Ruth Aitken and Wai Taumaunu when Australia were starting to dominate.
Wing attack Temepara George was replaced by the mercurial Liana Barrett-Chase, while a well-disguised but superbly executed injection of Anna Scarlett at wing defence for Joline Henry really paid dividends.
Muir said Aitken and Taumaunu had shown "tremendous courage" with their substitutions.
"Anna Scarlett was a menace, and just disrupted that attack end. She didn't always get clean ball, but she was very annoying.
"And Barrett-Chase fed some good ball in with great patience."
Muir waxed lyrical about the Silver Ferns' third quarter, where they ran rings round Australia and bounded out to a seven-goal lead at one stage.
"That third quarter: you'll never see skills like that. That was the pinnacle of netball as we know we can have it. There was no quarter given, both teams really at it -- just brilliant."
But the major plus from the win came in the realisation that the Silver Ferns had the grit to grind out a win when the pressure was on.
"We should be really proud of the girls as great athletes -- they've trained hard and they never let up. They were still working with that intensity right to the end, and that's something we've been looking for for a while.
"They showed the mental toughness we've needed."
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