"They'd gone and got fruit the day before but she wasn't allowed to go with the older ones. But that day she was allowed to go," Baker said.
"Once [her grandmother] went past and realised the baby had fallen out, she knew the damage was done and she couldn't change nothing. She just broke down on the road next to the baby."
Tapu loved the outdoors and could often be seen feeding animals or helping her dad in the garden.
"She was really tomboy-ish," Baker said, "and just prior to all of this happening, the girl really started to blossom - wearing dresses and looking all pretty. That side really started to come out."
Tapu's immediate family were deeply affected by their loss.
"They live just by candlelight and stuff at their house so it's quite a tight little whanau unit, so as soon as someone's not there they're going to notice there's only six people in the house instead of seven," Baker said.
"I think they're really starting to notice she's gone, now that it's a quiet time. They've got a missing person at their table, missing person in the bed."
Hundreds attended Tapu's tangi at Hiruharama Marae on March 1.
Senior Sergeant Maui Aben, of Gisborne police, said the investigation was being carried out with input from the serious crash unit.
"We're looking to see whether or not we are going to lay any charges and that's why we are investigating."