Highnam compared it to a coke bottle, where things slowly shake up and then pop out in an "explosive meltdown", she said.
She said it had affected the young girl a lot and had "added to the stress of the lockdown".
Little things like not being able to go to the park were extremely hard for Tara to understand, so a traumatic incident like this was devastating for the girl, she said.
The family's gate had been extensively damaged and Highman had needed to tie up the fence as it was a safety issue for her daughter, she said.
Police were called to the incident on Ōtūmoetai Rd about 1.30pm yesterday, a police spokeswoman said.
A car reportedly collided with a fence, gate and a power box. Police were making inquiries into the circumstances of the incident, she said.
This month was Autism Awareness month and Highnam said this was a clear example of how seemingly small things can cause extreme confusion and problems for those with the condition.