"Let them tell their story," she said.
It would ensure the commission's findings were robust, she said.
She has also asked to see the commission's final report before it is widely distributed in order to safeguard the right of Mr Whittall, who faces court charges. to a fair trial. However, the commission has said it must report to the Governor-General, and no one else.
Families' spokesman Bernie Monk said if the commission had to reconvene, "so be it".
"What has to be done, has to be done, for the sake of finding out the truth."
Families' lawyer Nicholas Davidson said it was a matter of ensuring all the relevant evidence came before the commission.
One person told the Greymouth Star the commission must not end up like the Erebus inquiry; everything should be dealt with fairly, not hidden away.
A note on the commission website said Ms Shortall's application "highlights natural justice issues".
- The Greymouth Star