"We were just speechless when they told us 'oh no we've got that wrong'.
"I've never been so pleased that someone's got something wrong," she said.
Jeffares struggled with the initial news and tossed and turned wondering how her family would cope.
But while the organisations involved are sympathetic to what happened, Jeffares has been in an ongoing battle to hold someone responsible.
The Hawke's Bay District Health Board conducted an investigation earlier this year and suggested she lodge a complaint to ACC.
In October she was told her claim had been denied, which ACC disputed - giving her "false hope".
Two months later, a spokesman confirmed to Hawke's Bay Today that the claim would be denied.
Clinical information was considered by radiologists, surgeons and medical and radiation oncologists who found there was "no clinical reason to doubt the original diagnosis of rectal cancer".
They sent the histology slides for a "blind reading" by five pathologists, and all of them said the original diagnosis of rectal cancer was reasonable (based on the slides), the spokesman said.
"None said a diagnosis of ovarian cancer should have been read from the slides. That another diagnosis was found during surgery for rectal cancer, did not mean Mrs Killarney had suffered a treatment injury.
"We understand this was not the outcome Mrs Jeffares was hoping for and we sympathise with her situation."
Her claim for a treatment for physical injury has been declined, which means her claim for treatment for mental injury has too, as it is dependent on the first claim, Jeffares' case worker told her.
She says the outcome has made her feel that what she went through was "for nothing".
"I'm pretty gutted. I don't know what path to take now."
She plans to seek legal advice and speak to the ACC advocacy service, which re-opens on January 20, but it all comes at a cost.