Truter said Kiwis had been unbelievably generous so far, but costs for offshore treatment could be high, so she encouraged potential donors to help before September 1.
Victoria Beacock issued the same plea. She's helped organise the Givealittle page for Auckland toddler Elyse Johnson, who also suffers from diffuse intrinsic pontine glioma.
So far $36,000 has been raised for Elyse as her family look to raise $400,000 so she can have surgery in Australia. "Hopefully we will have gotten enough before [September]," Beacock said.
Givealittle started in 2008 and the Spark Foundation began funding it in 2012. Since then donations have grown from $500,000 to $22m a year, sending costs spiralling.
Its biggest campaign raised more than $2m to buy Awaroa Inlet Beach in the Abel Tasman National Park.
In the past year, the Spark Foundation gave $1.7m to Givealittle, but that will likely drop to between $500,000 and $1m this financial year.
"Givealittle's success has been phenomenal ... This comes at a cost," said chief giving officer Tom Beyer.
He said the levy would be used solely to cover costs, such as customer service and website development staff and outsourced payment processing and website hosting.
These costs equalled about 8 per cent of donations, Beyer said.
Sheridan Bruce of the Fundraising Institute said the site had done well not to introduce a levy earlier.