Australia went up 2-1 in the five-match series with a 36-33 win in Brisbane last Sunday.
The game was characterised by tenacious defence with both sides' shooters struggling to overcome some tight marking.
Even the incomparable van Dyk had an off night.
Van Dyk's opposite, Susan Fuhrmann, used her 6cm height advantage to shut down the shooter's space and cramp her shot.
Van Dyk's return of 16 from 22 was well below what netball fans have come to expect.
Aitken, though confident her charge will bounce back, has asked for more movement from the world's best shooter.
"It wasn't her best day at the office at all and she is very mindful of that," Aitken said.
"She has gone back to look at what she can do. She is a true professional and won't want a repeat performance of that at all.
"We will continue to tweak things but we do need Irene to be able to adjust her game when needed."
That means the 37-year-old will have to partly abandon her holding style and move more to escape the close-quarter man-on-man marking the Australian defence is using to great effect.
Whether she can change her style effectively remains to be seen.
But what is certain is that the team relies heavily on her to slot the goals.
When van Dyk is not firing, the side struggles. It is a point not lost on Aitken.
With the Commonwealth Games next year and the world championship in 2011, Aitken would like to blood some young shooters in preparation for the post-van Dyk era, but players of similar calibre are not coming through the ranks.
Four of the next best shooters in the country are either not available or ineligible.
Former Silver Ferns shooters Donna Wilkins (retired), Daneka Wipiiti (pregnant) and Jodi Brown (family commitments) are unavailable, and Mystic shooter Cathrine Latu is not eligible because she has represented Samoa.
"One of the challenges for the [ANZ Championship] franchises is the shooting area tends be an area where they go for experience. You can understand why . . . but if you actually go through the starting line-ups of the five franchises, there is not that many available.
"That is a huge challenge for us because we don't have other shooters getting exposed to the ANZ Championship," and the step up from the national championship sides was too big, she added.
However, Aitken said, it was nothing new, as shooting depth was often an issue.
"At different times we have only taken three shooters on tour because we have not had the depth there."
On the bright side, it is hard to imagine van Dyk shooting so poorly again, and Australia is still missing defensive colossus Mo'onia Gerrard and the promising Laura Geitz.
A big crowd at Stadium Southland should help as well, Aitken said.
"It is still two goal posts and a wooden floor.
"It is what you do on it, but I do think the players will get a lift from playing at home and feeling that crowd support."
New Zealand v Australia
Invercargill, 4pm tomorrow
New Zealand: Casey Williams (captain), Temepara George (vice-captain), Katrina Grant, Paula Griffin, Joline Henry, Laura Langman, Sheryl Scanlan, Wendy Telfer, Anna Thompson, Maria Tutaia, Irene van Dyk, Larrissa Willcox.
Australia: Sharelle McMahon (captain), Kate Beveridge, Julie Corletto, Catherine Cox, Johannah Curran, Susan Fuhrmann, Kimberlee Green, Renae Hallinan, Lauren Nourse, Susan Pratley, Amy Steel, Natalie von Bertouch.
