Her brother took her to the doctor in Wairoa on the Friday before she died for a check-up and to find out the new date of her operation, May 17.
Her health deteriorated over the weekend and the family called an ambulance at 4am on the Monday because she couldn't breathe, he said.
"It all just happened so fast from here to the hospital.
"I just watched my sister suffocate."
A post mortem found Gilbert had an undiagnosed chest infection, aggravating her enlarged thyroid.
Now her family wants to know why the chest infection wasn't picked up at the doctor and why the surgery was postponed.
A meeting has been scheduled between the Hawke's Bay District Health Board (HBDHB) and the family for June 11 to discuss what happened.
"I just want them to say to our faces that they failed us and their system needs to be sorted out," her brother said.
"I want to know why the first surgery was cancelled and why on the Friday they didn't pick up the chest infection.
"I'm really mad."
Gilbert, who grew up in Waikaremoana, was a shy and loving woman with a "very big heart", her brother said.
"I could tell her anything ... we were very close."
"She was a focused young lady, she had dreams and goals.
"She focused on what she wanted, her dreams were to travel and buy a house."
Gilbert's family received a letter from HBDHB Communities, Women and Children service director Claire Caddie on May 23.
It stated the DHB had initiated a review to find out what happened and why it happened "so that, if possible, we can take appropriate action to reduce the likelihood of a similar event occurring in the future".
HBDHB chief medical and dental officer Dr John Gommans said he could confirm a woman presented to Wairoa Hospital's emergency department on Monday, May 14.
"Despite all efforts made by the medical team, this patient sadly passed away.
"The DHB's thoughts are with the woman's family and friends at this time.
The DHB is investigating the death through its Clinical Event Review process and has referred the death to the coroner, he said.
"A meeting with the family has been set up so we can understand their concerns and discuss the review process with them.
"The coroner's office has ultimate jurisdiction and its process is independent and external to the DHB."
A funeral was held for Gilbert on Friday, May 18, and she was buried at Orangitirohia urupa.