But donations from readers - including a $10,000 cheque from an anonymous supporter - have seen the family's $16,000 double.
"It's been fantastic and it just shows you what people are like," mother Jade Riley said. "We've also been getting some very inspirational emails and comments from a lovely lot of people on my Facebook page, Zahnee's Cause."
Ms Riley said it was relieving to know there was finally a date for the operation - September 22 - which her family had been battling toward for years.
"At the same time, it's all very nerve-wracking for us at the moment. We're pulling it all together, but at the end of the day, she's going to have that major operation and as parents, we've done our very best."
People wishing to help can donate to the ASB account "Zahnee's Cause", account number 12-3217-0140729-00, or send messages of support to the Facebook site, Zahnee's Cause, or to Zahnee's parents at paulnjade@xtra.co.nz.