The teacher went back to work last March. In hindsight, she was still physically and psychologically unwell at this time, the Tribunal said.
In March last year, the senior teacher confronted her husband about "intimate" text messages between her husband and another person.
Disharmony soon followed, and the couple temporarily lived apart.
Soon, the senior teacher identified a friend and colleague as the other party in the intimate texts.
The complaints assessment committee said the senior teacher "genuinely and with cause" believed an affair was going on.
The situation escalated, with the senior teacher confronting her colleague several times in March, April and May.
The Tribunal said the senior teacher had also told the school's co-principals she believed her colleague "might have been using a school computer to find men."
The co-principals said she also urged them to reconsider the junior teacher's appointment, although the senior teacher did not recall making any such comment.
The Tribunal said on some occasions the senior teacher used "offensive language" in the confrontations. In one instance, the junior teacher recorded an exchange on her cellphone, and children could be heard playing nearby and approaching the two adults.
That encounter entered calmly but in May, according to the Tribunal, the senior teacher found photos of her colleague and "intimate e-cards" on her husband's computer.
She confronted her colleague, who then decided to report the run-ins due to fears of "ongoing conflict."
The teacher was stood down, then resigned in late May.
The Tribunal said the senior teacher had a "commendable record" before her health problems and flare-up with the colleague.
It also said the teacher's depression, following her illness and the steroids' side-effects, limited her capacity for emotional restraint.
The Tribunal said the senior teacher was clearly guilty of serious misconduct. It said the senior teacher's confrontational behaviour was likely to adversely affect student well-being.
The teacher was censured and ordered to pay 30 per cent of the complaints assessment committee's costs for the case.
The Tribunal heard the senior teacher had since started therapy, her health had improved, and she had found a new job. Her new principal was aware of last year's events and supported her, the Tribunal said.