Arlia broke her leg in three places and was admitted to Starship Hospital.
Her mother, who suffered a broken hip and other injuries was in a stable condition at Auckland City Hospital.
The family was heading to Gisborne to find work, Mr Brass said.
"They were going down to have a look and try it for three weeks and, if they liked it, they were going to come back and pack up the house and go down."
The family were already having a stressful time, with Vance's sister critically ill in Middlemore Hospital from complications from a gall bladder operation, he said.
"We don't know if she's going to make it or not."
Mr Brass said Ms Niwa must have fallen asleep while she was driving.
"It would have to have been that because she was a real good driver and a church person and wouldn't break any rules."
She was devastated at the crash, he said.
Ms Niwa had been trapped in the vehicle and suffered leg injuries, but was now in a stable condition at Whakatane Hospital.
Mr Brass said the whole family was shocked at the incident, but knew the outcome could have been worse.
"We lost one, but still, we could have lost them all."
Tributes to Varnah have appeared online.
Staci-Lee Smith wrote: "It is with our deepest regrets that we mourn the loss of our baby niece Varnah and send our love and prayers to Heidi and Aliyah (sic) at Starship Hospital in Auckland, hoping for a safe recovery!"
Robert Heke Jr wrote: "R.I.P Varnah Brass, the lil infant that died in the head-on collision in Thornton, our thoughts are with you and the family."
And Chelsea Dou'ble wrote: "R.I.P little Varnah Brass. Never got a chance to grow up. Condolences to the whanau."APNZ
