A NSW mother injected urine into her immune-deficient daughter before police uncovered used syringes and urine sample jars in her handbag, a court has been told.

The 47-year-old woman - a former nurse - pleaded not guilty in Newcastle District Court to three counts of using poison to endanger the life of her daughter between December 2013 and March 2015.

In an alleged poisoning episode in March 2015 - when the girl was nine - she became acutely unwell with deteriorating renal function in Westmead Children's Hospital in Sydney, the court was told on Monday.

Blood cultures showed a "sudden, unexplained increase" in chemical waste products urea and creatinine, crown prosecutor Wayne Creasey SC said.

"The evidence will establish, I expect, that the accused was almost always at (her daughter's) bedside during her admissions," he said in his opening address.

"I expect a clinical microbiologist ... (will) support the contention that the accused interfered with the indwelling intravenous central line by introducing urine to the line."

The other two charges relate to hospital admissions in early 2014 for constant diarrhoea and vomiting.

A gastroenterologist is expected to say the diarrhoea was "factitious and likely caused by the surreptitious administration of a laxative agent," Mr Creasey said.

He said the girl, born in 2005, has a genetic condition and an associated immune deficiency.

Between the age of two and nine, when police intervened, the girl was regularly admitted to hospital with serious conditions later resolved with medical intervention, he said.

"The senior doctors at John Hunter Hospital and Westmead Hospital became concerned that some of (the girl's) admissions were as a result of deliberate harm by the accused," Mr Creasey said.

Police who interviewed the mother in March 2015 discovered two empty urine sample containers, medical equipment, a syringe containing a liquid, five used plastic syringes and a stool sample container in her handbag.

The mother - who had multiple children - denied ever giving her daughter laxatives or injecting urine and said she'd gathered the medical supplies when her daughter was being transferred to a new hospital.

She told police she "missed being a nurse" and liked "being involved" in her daughter's care, the Crown said.

The trial before Judge Christopher Robison continues.