She was also seven months pregnant and the unborn baby did not survive.
With Talla's birthday approaching, her mother - as well as Tane and Aka who are now 14 - spent time tidying up her grave.
Returning the next day, Gwyneth noticed a plaque, string of solar lights and pounamu necklace had been stolen.
"We have cemented down most of the pounamu," Gwyneth said.
But it was not the first time she has been "heartbroken" by thieves.
About three years ago, two pounamu pieces were stolen from Elwyn's grave.
One of the items was later found for sale on Facebook, with the offender admitting to police it had been sold for $300.
The other pounamu item was never recovered and the offender was not charged, making Gwyneth feel reluctant to report the recent thefts.
"We were just given the stuff back and never heard anything more about it.
"I just didn't want to deal with that again.
Gwyneth's aunt also had four steel roses taken shortly after she had placed them on her husband's grave at the same cemetery.
"That really broke my heart because she probably used her pension to get those," Gwyneth said.
Talla and her sons were subjected to family violence when she was alive.
Her sons now advocate against domestic violence, sharing their stories through singing and speaking at community events and a Ministry of Justice summit last year.
"It's really heartbreaking - (Talla) has already been violated and now she should be resting in peace and then they come and do that and then that violates her too," Gwyneth said.
"Being Maori, I just don't understand. It's so wrong to take things from the cemetery, let alone pounamu."
She hopes the Christchurch City Council will consider installing security cameras throughout the cemetery.
City council acting unit manager for parks Al Hardy said family and friends are responsible for items on graves.
"Council would ordinarily only remove broken or neglected items or materials that represented a health or safety issue."
He encourages people to report thefts to the city council contact centre. Over the past year, he says five have been reported.
"There have been no steps taken for theft of items from grave sites.
"For added security following the March 15 tragedy, the Memorial Cemetery has camera surveillance."
Mr Hardy said extra security measures would be considered on a case-by-case basis.