The Brunei government found Dr Susan Lim's fees "exorbitant and unjustified", said lawyer Alvin Yeo in his defence of the Singapore Medical Council's disciplinary committee's verdict that she was guilty of professional misconduct for overcharging a royal patient.
Mr Yeo told a Court of Appeal on Tuesday that from May to June 2007, the patient was in the intensive care unit and being looked after by the doctors and nurses there.
"In this period, Dr Lim's fees extraordinarily increased to $250,000 to $450,000 per day, essentially for visiting the patient and monitoring her status while she was in the ICU under the care of other doctors," he said.
That Dr Lim did not know there was a rule prohibiting overcharging was "both unbelievable and shocking", he said.
She is appealing a three-year suspension and $10,000 fine imposed by the SMC.
The Appeals Court will give its verdict at a later date.
Mr Yeo also dismissed her argument that she had an agreement with the patient about the high fees.
He said the Brunei government had in the past paid those high bills, not because they thought the fees were fair but because of the trust they have in Singapore doctors.
On the argument that the fees charged reflected the business cost to Dr Lim, Mr Yeo said: "Just because it costs $X to operate Dr Lim's various clinics, that does not give her the right to charge $X, irrespective of the services actually rendered."