The 42-year-old allegedly cut gas and water mains at Kareena Private Hospital at Caringbah, in Sydney's south, just after midnight on Tuesday before setting off the fire hoses.
About an hour later, she allegedly crossed the road to Sutherland Hospital and switched off the medical gasses, forcing the facility to switch to portable oxygen and air for two hours.
Police arrested the woman in the neighbouring suburb of Miranda just before 4am for a breach of bail.
The woman has been charged with several counts of public nuisance, sabotage, trespassing and tampering with fire alarm.
She was refused bail to appear in court on Wednesday.
"I can't stress enough how catastrophic and serious in nature this could have been," NSW Health Minister Ryan Park told reporters.
"To do this in any way, shape or form, is to put the lives of some very seriously ill people at risk in a hospital.
"It's not a joke, it's not a laughing matter, it's not a prank, it's not something that should be underestimated."
There was no impact on patients at either hospital and Ramsay Health Care, which runs Kareena Private Hospital, said the facility had continued to operate as usual.
"All services were quickly restored with minimal disruption and no impact to patient care," a spokesperson said.
The alleged sabotage showed the need for the government to invest in hospital security, Health Services Union NSW secretary Gerard Hayes said.
"The threats facing our hospital security are greater and more unpredictable than ever before, yet the resourcing is simply not keeping up," he said.
"Protecting critical infrastructure like medical gas systems must be a priority."
Sutherland Hospital has 375 beds, while Kareena Private Hospital is a 142-bed facility.
The NSW government said it would review whether security improvements needed to be made following the incidents.
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