Mr Wilson said the new board and the change in the manager's title "indicates a more corporate approach".
The other board members are Sir Owen, former OTS executive Tony Holt, Wellington tax lawyer Dr Geoff Harley, former Race Relations Conciliator Greg Fortuin, and Donna Grant, a Rotorua-based director of the Warriors league board, who tapped Ms Rei to take over.
Mr Wilson, who resigned from the Supreme Court after being accused of a conflict of interest in 2010, said there had been "a breakdown in the relationship between Sir Owen and Ruth".
He acknowledged "the very good work that Ruth and her team have done", and said the $2 million budget Sir Owen earmarked for the inquiry was intact.
But the falling-out with Ms Herbert is a blow to Sir Owen's goal of developing an "evidence-based blueprint" for tackling child abuse and domestic violence which he planned to take to the UN.
Ms Herbert, 60, has been a passionate campaigner on domestic violence and other issues since she fled from a violent relationship with "a loaded gun at my head" in the 1980s.
She was plucked by Sir Owen to manage the inquiry last September, three months after the end of her previous job, as director of the Ministry of Social Development family violence unit.
Ms Trask is a former family violence co-ordinator for the Hauraki area and later also worked for MSD.
Ms MacLennan said last night that the two women were "essential to a constructive outcome to the inquiry".
"I joined the think-tank to work with them and the other talented and committed New Zealanders and people from around the world, as I believed this was the best opportunity in my lifetime ... to take constructive steps to address domestic violence and child abuse. I am not able to continue my involvement without their involvement."
Another think-tank member, Waikato University psychologist Dr Neville Robertson, said: "I think shock is not too strong a word."
Dr Annabel Taylor, also on the think-tank and director of Canterbury University's Te Awatea Violence Research Centre, said Ms Herbert was "a person of great integrity" and she assumed there were "some pretty big issues" behind her departure.
Glenn inquiry
• NZ's first independent inquiry into child abuse and domestic violence.
• Set up by Sir Owen Glenn with $2 million budget.
• Executive director Ruth Herbert appointed September 2012.
• Inquiry was to end this year, now due late next year.
