Bennett called for Ardern's and Robertson's actions to be included in the terms of reference because a key issue was what they were told about the sexual assault complaint and how they responded.
"It's the only way it's going to clear the whole thing up, and it's about justice for the complainants."
But she had no faith that their actions will be scrutinised.
Robertson was reportedly told about the sexual assault claim at the end of June, but he has not commented on when he was told about such a claim, citing the QC process and the complainants' privacy.
He said last week that he had not been contacted by Dew, but would speak to her if asked to.
Ardern has said that a report in The Spinoff on Monday was the first time she had seen such a complaint from one of the complainants, suggesting that any previous complaint she was told about had been laid second- or third-hand.
She has said that the terms were being drawn up with the complainants, and their wishes should be paramount.
Ardern has remained tight-lipped about the terms of the ex-staffer's resignation, saying on Friday that she would not comment beyond saying she had received the resignation.
The ex-staffer's contract with employer Parliamentary Service would have included a "relationship breakdown" clause which, if invoked by Ardern, would usually have entitled him to three months' salary.
Bennett said that Ardern should come clean and say whether the ex-staffer was getting a payout.
She accused Ardern of hiding behind the Dew review, noting that Labour had also failed to release its report into its handling of the sexual misconduct claims at the Young Labour summer camp at Waihi last year.
"They just should have learnt lessons from the past and just be telling everything they know, rather than wiping their hands of it and trying to move it on," Bennett said.
Ardern has offered to meet the complainants, but it is not yet clear whether this offer will be accepted.