The family had hoped McDonald's in Botany would be able to access CCTV footage to find out what happened to the toy.
But Mandy Archer-Page said she was appalled to learn today the store's security camera system had been broken since last Monday.
She said it was "ridiculous" the CCTV was down.
"The fact that it hadn't even been addressed or dealt with for three days I think is pretty slack really," she said. "You're supposed to have it on for security reasons anyhow."
She said the Botany store had offered her an apology, but it was "too little, too late."
McDonald's today had no idea what happened to Bunny and confirmed the Botany store's entire CCTV system was under repair.
"It's been described to me as a fault in the technology," company spokesman Simon Kenny said. "...It's been down since last week, unfortunately."
He said there was no footage of the time Bunny was left behind.
"Unfortunately in this case there's nothing there," Mr Kenny said. "It sounds like some people had seen it in the area where they'd been and by 7 o'clock that night it had gone."
Mr Kenny said the store policy was for goods found in the restaurant to be put in a storage area that day, and then in the manager's office with other lost property until the owner returned.
He did not know how long it would take for the CCTV system to be fixed or how complex the fault was.
However, McDonald's Botany had put up "lost" posters in the restaurant and hoped this might help.
Mrs Archer-Page hoped today's publicity would help convince whoever had Bunny to come forward. She said no parent wanted their child to suffer and it was upsetting to see Darcey so distraught.
The family were offering a reward of another soft toy, much like those they had tried without success to get Darcey to adopt.
The family also printed flyers to help reunite Bunny with Darcey and set up the Facebook page "Bunny is Missing" to help find the toy.
