It will only be mother and daughter making the trip, and a GiveALittle page has been set up to help.
"We asked Air New Zealand to help out but they said no - even after their big profit. Even if they could offer staff prices that would be nice," Lisa said.
"At the end of the day we are going and we will mortgage our house to get there. It's not if we're going. We are going."
As well as hosting a GiveALittle page, Lisa is also hosting a movie night on Saturday, September 25, to which the public are invited.
Ava will be among the first Kiwis to receive the new treatment, and Lisa said results so far in other patients had been encouraging.
Currently Ava is reliant on Botox injections, which have to be delivered under local anaesthetic - a treatment Ava will no longer need after her surgery.
"These treatment lasts about three months but we are lucky if we get in every eight months," Lisa said.
The full treatment will likely involve two separate surgeries, costing around $80,000, and then Ava will have to undergo several weeks physiotherapy.
"She won't be able to walk for a few weeks," Lisa said.
Although in mainstream schooling, Ava's mental development is a couple of years behind her classmates, and Lisa said she would have to pick the right time to explain the procedure.
"She gets really anxious. With Botox she freaks now that she knows what that's about. We will talk to her about it, but at the moment she's happy she's going to America with mum and we might be going shopping."
Ava herself said she was most excited to try out some of the waterslides in Saint Louis.
"I haven't told her yet but we won't be able to go in water for four weeks. Hopefully we can find a slide before the procedure," said Lisa.
If you would like to donate visit givealittle.co.nz/cause/chasingavasdream. If you would like to attend Ava's movie fundraiser you can buy tickets for children's movie Storks at 3.30pm on September 25 at facebook.com/chasingavasdream