Doctors became suspicious when the child stopped showing symptoms in hospital.
After this incident, Oranga Tamariki removed both of the woman's children from her care, but during a supervised visit nine months later she either fed the boy a round button battery or placed one within reach so he could swallow it.
She was not allowed any access to the children after this.
The offending against her daughter began in 2012, with the woman repeatedly taking the girl to visit doctors, hospitals and A&E departments, reporting she had rashes, fevers, and was suffering from seizures.
The victim was generally not suffering from any such ailments, but was prescribed medications and a sedative.
"Because [the child] did not need any of this medication, ingesting it was extremely dangerous," the Court of Appeal decision said.
The girl was also exposed to "major and invasive investigative procedures" as clinicians struggled to pinpoint the cause of the symptoms her mother was reporting.
These included blood tests, MRI scans, and two lumbar punctures under anaesthetic. She was hospitalised several times, including an 11-day admission in Starship and a week at Waitakere Hospital.
She also administered a mind-altering seizure medication to the girl, and on another occasion gave the girl a powerful sedative before calling 111.
"The recording of the appellant's exchange with the operator suggests that the appellant was not panicked or anxious, but rather cheerful and even jovial."
In her appeal against the sentence, the woman argued the discount she received for having FDIA was not large enough. The original sentencing judge allowed a discount of 30 per cent from the sentence starting point.
The appeal judges made the point the offending would not have happened if it were not for the disorder.
"She is the victim of an obsessional, needful, narcissistic disorder that ties her own self-worth to the dual need for high vulnerability in her children, and sympathy from others," the decision read.
"If that vulnerability is not present in fact, then she must manufacture it by harming the child."
However they pointed out she was not "robbed of all will and self control", which was why she could not plead insanity.
They said the relationship between the disorder and the offending, as well as FDIA's "corrosive" effect on the ability to choose not to offend, meant the discount could have been as high as 50 per cent.
"This is to recognise, in a rough and ready way, that FDIA is structurally responsible for this offending, as is the appellant.
"We reiterate that apart from the FDIA, the appellant was a good mother and a thoroughly law-abiding citizen. This is a clear case in which the full 50 per cent discount is justified."
The judges also allowed a further discount to sentence for the struggles the woman had been through in prison, including being assaulted and not receiving dental treatment for nine months after the assault.
She is in voluntary segregation for her own protection, which means she cannot receive effective treatment or rehabilitation for her disorder.
The judges allowed a further 20 per cent discount for the burdens of sentence and the need for rehabilitation and reintegration.
The Court of Appeal quashed the original sentence and replaced it with one of four years' imprisonment.
