Brown said her family, including six young children, were distraught at the loss of Buttons, who was a rescued wild cat and had "just become smoochy".
They didn't even have a photo to remember him by. The family paid $195 for the three cats to be desexed and were told the SPCA would credit Brown's account $40 for Button's operation.
SPCA vet Jonathan Steel-Carroll said Buttons "went ballistic" as he came out of anesthetic. He was put in a cage with other wild cats and was accidentally put down.
"This is not a case of a friendly family moggy that has been euthanised," Steel-Carroll said.
Steel-Carroll said the SPCA regretted the error and now put a fluorescent red marker on the cages of cats to be euthanised.
The SPCA offered to cremate Buttons but Brown collected his body to bury at home under a fruit tree. "I was scared they would lose his ashes." Kirsty Wynn