Charlotte 'Lottie' Paluszak's death on November 11 last year came as a terrible shock to her daughters Petra Anderson and Monika Simpson.

Now, almost three months later, the truth behind the 84-year-old great-grandmother's suspicious death is starting to unravel as police investigate the Carinity Fairfield Grange aged-care home in Townsville, Queensland.

According to Lottie's death certificate it was dementia and diabetes that took her life but her family aren't buying this now and want to know why their mum is dead.

Charlotte "Lottie" Paluszak died on November 11 last year, raising suspicions with her daughters.

"She can't rest in peace until we find out what did actually happen to her," said Monika in an exclusive interview with A Current Affair .

"To die of her diabetes you know - dementia complicated diabetes - that was the bit that floored us, (it) didn't make any sense."

To make matters worse, the Paluszak family are not alone in this fight for the truth, with staff reporting four other suspicious deaths taking place at the home.

Since the investigation launched in November 2017, three nurses have been dismissed for failing in their duty of care.

A senior nurse was seen photographing Lottie's coffin at her funeral.

That's all the sisters have been told so far but they say it doesn't answer their question: "Why is our mum dead?"

"The people have been sacked but it doesn't bring mum back," Monika said.

What the sisters do know now is that a senior nurse is at the centre of this investigation.

When the camera was switched off, former staff have told A Current Affair that they were shocked when that nurse allegedly gave Lottie an injection of Schedule 8 drugs the day before she died.

Monika Simpson said their mother could only rest in peace when the truth came out.

When management became aware of a breach of procedure they immediately sacked those involved and called the police.

However, the only information the Paluszak family received on this until recently was the bill.

"There were large amounts prescribed for her, I'm not sure how much she was actually given of that, but there was large amounts, which I thought was quite unusual," Petra said.

According to Monika and Petra, this same nurse was there during one of the most intimate moments of their lives - their mother's funeral held at the aged care home.

Daughter Petra Anderson is demanding answers about her mother's death.

The sisters' suspicions were raised when a family photo at the funeral revealed the nurse taking photos of Lottie's coffin as it was leaving the building, which they said they believed was inappropriate.

"I've taken some photos because I'm sending those to family overseas so I don't know why anyone else would want to take a photo of mum... mum's coffin?" said Monika.

"It seems strange. She has no affiliation with us and she wasn't doing it for us."

Just when things couldn't get any stranger, when the cameras were turned off again former staff told A Current Affair that not only did this nurse record Lottie's funeral, but she was also seen to be doing what they describe as a "happy dance" while standing in line.

The bill shows Lottie was given a large amount of Schedule 8 drugs.

"I didn't see the happy dance. I thought I saw someone put their hand out and touch the coffin as we went through a guard of honor of nurses, but nothing stands out like that," said Petra.

Sadly, according to Leanne McDonald from Shine Lawyers, cases like Lottie’s are not isolated and demonstrate the need for video surveillance in nursing homes.

"It's also very sad for the residents because this is their home and they can't escape if there's bad treatment there," she said.

With the family left in the dark, their only hope is now in the hands of the police, Coroner’s Office and the Health Ombudsman.