Staff refused to carry out the operation unless the kitten's right eye, which was severely infected and ruptured, was also treated.
"The kitten's right eye had a large, dry mass protruding from it and was oozing thick, yellow fluid," the SPCA said.
"The kitten was hunched and pulled away from any attempts to touch her head, indicating pain and distress."
After several unsuccessful attempts to contact Forde, staff at the clinic called the SPCA, who seized the kitten and transported her to its specialist clinic.
The eyeball was in such an advanced stage of injury that removal of the eye was the only treatment option, the SPCA said.
The eye rupture was likely a result of infection that had been left untreated for up to two months, the SPCA veterinarian said.
"During that time the injury would have been very obvious and any layperson would have recognised the need for veterinary treatment. It would have been painful and distressing for the kitten and could have been alleviated with treatment."
The veterinary clinic's records show the ruptured eyeball had been diagnosed on February 5, but Forde did not come back to the clinic until March 8, when she wanted the cat desexed.
SPCA Auckland chief executive Christine Kalin said the woman's excuse was "utterly unacceptable on every level".
"The defendant says she could not afford to have the kitten treated and was unwilling to surrender it to SPCA Auckland. So instead she did nothing hoping it would all just 'go away'.
"When you take on the care of an animal you are totally responsible for its wellbeing. If animals in your care need help and you fail to seek treatment for them, then you are guilty of neglect and cruelty and we will prosecute you."