However, she was "absolutely delighted" to take over the "wonderful facility".
"The mission really opposed the closing of the school, so it's a bit ironic that we are now moving in," she said.
The organisation took over the site in May and would move in on July 14, before a grand opening on July 21.
"Moving down here is fantastic. We will be able to offer a lot more services."
One-third of the school will be developed into an early years services hub, and the remainder will be used by Little Citizens early learning centre.
Both facilities at present occupied buildings that were at the end of their useful life, on a much smaller site in Wesley St.
Ms Nash was excited about being able to offer families midwifery support, antenatal and breast-feeding classes, a toy and book library, playgroup facilities and a community garden.
With support from Mercy Hospital's charitable trust, a family kitchen would also be installed to provide cooking lessons.
Little Citizens manager Lisa Foster said the move was "brilliant for our children and our families".
"We are the only early learning centre that's the size of a school," she said.
Highlanders rugby players joined forces with Delta staff to build two safety fences and clear a garden space at the grounds yesterday.
Highlanders commercial manager Mike Kerr said community engagement was important to the team and it was a "point of difference" for it.
By teaming with partners such as Delta, the process was more effective and meaningful.
"It's something we consistently want to do," he said.
Delta chief executive Grady Cameron said the company was "delighted to be involved in the redevelopment of the old Forbury School grounds as a warm, welcoming place for families with young children".
"It's a great opportunity for us to give practical assistance to provide a safe environment for children to play."
