Brittney's initial symptoms included vomiting and a sore throat, Lorraine Conway told ABC News.
A few days later, she complained of chest pain and began refusing food, appearing to be in agony whenever she tried to ingest solids. Brittney was taken to Robina Hospital on the Gold Coast, where the doctor guessed she had a virus.
Despite asking for an x-ray, "No x-ray was ever done", according to Lorraine Conway.
Nine days after first showing symptoms, hearing her daughter cough during the night, Conway got up to check on her.
"Brittney was lying in a pool of blood, unconscious," she said.
After the youngster was rushed by ambulance to the Gold Coast University Hospital, she was finally x-rayed and the battery was found.
After suffering through nine hours of surgery to remove the battery, doctors were unable to stabilise her and Brittney was transferred to Queensland Children's Hospital.
There, she underwent further surgery, but eight days later died from her injuries.
"She just had a beautiful nature … just a really content and happy little girl," Lorraine Conway said.
"She had a thousand sparkles in her eyes."
Queensland Health has advised it is carrying out a review of Brittney's death and extends "sincere condolences" to her family and friends.
Brittney's tragic death has reignited fierce debate around regulation of the common household items.
Kidsafe chief executive Susan Teerds said the regulation of button batteries was critical.
"For 40 years companies have been dumping these, what I call landmines, into our homes and they've known they're problematic," Teerds told ABC News.
What to do if your child swallows a button battery
Every day in Australia at least one child is hospitalised because they have swallowed a button battery.
The most common age for this is between the ages of zero to 4 years old, with body regions affected including the bowel, oesophagus, nose and ear.
The small, shiny batteries are often used in common household items including TV or key remotes, scales and toys. Once swallowed, they start to burn internally, causing lifelong injuries or death.
If your child ingests a button battery you should call NZ emergency services immediately on 111 if they are having any trouble breathing.
If they are not having trouble breathing, parents should:
• Call the NZ National Poisons Centre immediately on 0800 764 766.
• Do not try to make your child vomit.
• Do not let your child eat or drink while awaiting medical advice.
How to keep batteries away from children
• All batteries should be stored in a child-resistant locked cupboard at least 1.5m above the ground.
• Check that all toys, remotes and other products that contain batteries have a screw to secure them, otherwise use strong tape.
• Throw old batteries away in an outside bin away from the reach of children.