The girl's symptoms included intermittent fevers, multiple sore joints with no confirmed history of injury, and weight loss.
Doctors treated the girl episodically and when X-rays showed no musculoskeletal cause for her symptoms, no further investigations were sought to explore the cause.
However, after an appointment with her usual general practitioner on January 18, 2019, the girl was taken to hospital.
A week later she was diagnosed with acute rheumatic fever (ARF) with severe mitral regurgitation and kept on strict bed rest until March 13, 2019.
Commissioner Anthony Hill acknowledges it would have been difficult in making the diagnosis as the presentations were unusual for ARF.
However, he has taken offence at The Palms for failing to investigate the girl's symptoms further.
If the doctors investigated further at the start, the girl could have been diagnosed and treated for ARF earlier than March 13, Hill said.
The failings showed "a pattern of poor care" across the practice for which The Palms was responsible.
Hill found the medical centre in breach of the Code of Health and Disability Services Consumers' Rights (the Code) for its failures of care.
The Palms was recommended by Hill to apologise to the family, which it has done.
Hill also thought The Palms should prepare a case study, anonymously, on the girl's care for training all clinical staff.
He also thought they should consider facilitating a regular clinical meeting for reviewing patients who have been seen over multiple providers over a short period with similar complaints, or for patients with an elusive diagnosis.
The Palms has taken on board the recommendations Hill has provided and was working through them, Dr Hayter said.
The girl's consultations took place during the early stage of a new management system at the practice which led to delays.
"For a brief window there was an absence of adequate process to relay casual patient notes in a timely fashion," Hayter said.
"This was quickly identified and remedied. However, in the interim, the lack of process contributed to the delay of diagnosis.
"We are sincerely apologetic and disappointed. We have conveyed our sincere apologies to the family."
The Palms also reiterated the "critical importance" of communication between their health professionals and administrative staff.