Police were called to the hospital shortly after 10:45 a.m. after a body was discovered in a vehicle, Orlando police Lt. Diego Toruno said.
"Security advised a white female drove up to the valet area (and) was argumentative and asking for medical assistance for a female passenger," Toruno said. "Hospital staff determined (the passenger) was deceased."
Police said the driver became combative and pulled out a knife. They said police officers and hospital security guards detained the driver without incident.
Deputies said Aleyda Rivera, who would have turned 12 Thursday, was stabbed multiple times. They said Rosa Alcides Rivera is a suspect in her daughter's death.
Rivera is in custody and charges are forthcoming, investigators said.
"At this time, we know the incident occurred in our jurisdiction at an undisclosed location," the sheriff's office said in a news release.
The hospital was placed on a brief lockdown and the main entrance to the hospital was closed for much of the day.
No other details were given.
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