The letter from federal health minister Greg Hunt provided details on new funding allocated for research into treating Diffuse Intrinsic Pontine Glioma (DIPG), an aggressive type of childhood brain cancer.

After a two-year fight, Annabelle succumbed to DIPG on Wednesday.

"Too little, too late for Annabelle," Kathie wrote in a post on the Love for Annabelle Facebook page.

"But we are proud that Annabelle has helped to save others. Perhaps this is her last selfless act that will continue to help others."

For two years following Annabelle's diagnosis, Kathie and husband Adam Potts fought for answers on why treatment options were so limited for their tiny daughter. They received no positive news despite sending more than 20 letters to parliament.

In Australia, DIPG accounts for the majority of the 30 to 40 children who die each year from brain cancer and is the main cause of death in children with brain cancer. DIPG is considered incurable.

After a round of radiation therapy, Kathie and Adam were told to take Annabelle home and "make memories". But in a desperate attempt to treat the aggressive tumour at the base of their daughter's brain, the family began flying Annabelle to Mexico for experimental treatment.

Sadly, nothing could save the preschooler.

"There are so many mixed feelings [about the funding announcement]," Kathie said.

"I’m angry that it took so long to come through. I’m angry that we had to fight so hard for it.

"I am absolutely gutted that it won’t help Annabelle. But as Annabelle got joy from doing things for people, I am happy that this will help other families and stop them having to fight as hard as we did.

"The hope for Annabelle is gone, but there is hope for the future DIPG children."

The government funding includes $592,388 for research into developing a CAR-T immunotherapy for DIPG. Dr Misty Jenkins at the Walter and Eliza Hall Institute for Medical Research has developed a prototype CAR-T immunotherapy specific to DIPG, which has shown to effectively kill DIPG cancer cells.

"I absolutely believe this new research will happen because of Annabelle," Kathie said.

While the letter from Mr Hunt was a blow to a family already in despair, the Potts family has received a huge outpouring of love from the Canberra community and the nation since the announcement of Annabelle's death earlier this week.

More than 9000 people have engaged with the Facebook post that notified the world the five-year-old had finally lost her battle with brain cancer on Wednesday morning.

One comment reads: "There are no right words. Congratulations on being parents to such an inspirational little girl. How lucky she was to be born into your family. Grieve wholeheartedly as you deserve to but don't ever give up her fight. Kids shouldn't die of cancer.'

And another: "Kathie and Adam, my tears are flowing as I read the post I was hoping never to see. I will never forget meeting Annabelle, her bright cheeky smile lighting up her face and the strength she showed in her fight."

Senator Cory Bernardi, the only politician to participate in Annabelle's Lemon Face Challenge on-site at parliament house in November, described Annabelle's death as "a tragedy".

"In the midst of such great loss, maybe we can take some comfort from the fact that Annabelle’s brief life prompted the federal government to invest further into research and treatment of Diffuse Intrinsic Pontine Glioma," he said.

"We can only hope that this investment and research into such a lethal disease will ultimately result in a cure."