Kim Wolfe, a 43-year-old Nassau County correction officer, was in custody awaiting arraignment on unspecified charges. Any court proceeding was likely to be delayed after she was later taken to the same hospital where the aide was shot, complaining of difficulty breathing. It was not immediately clear whether she had a lawyer.
The alleged shooting spree occurred on Wolfe's day off.
"It does not appear this was a random act," Nassau Police Lt. Kevin Smith told WCBS-TV in New York. "There was some kind of relationship between these two...it appears there may be a domestic element."
Stacie Williams, 45, a nurse's aide who worked the night shift in the maternity ward of Nassau University Medical Center, was found shot multiple times at about 1 a.m. while on a break outside the Long Island hospital's visitor's entrance.
In the other shooting about 3 1/2 miles away in Hempstead, Wolfe's 56-year-old uncle was fatally shot, Lt. Smith said. Her grandfather was shot in the leg.
Wolfe also abducted her 23-year-old niece before fleeing the scene in a car, Smith said.
Police pulled over the car at 5:45 a.m. and Wolfe surrendered peacefully, Smith said. Her niece was not harmed.
Police said the suspect was armed, and they would test the firearm to determine whether it was used in the shootings.
A Nassau County homicide detective told reporters that Wolfe and Williams had a romantic relationship.
"They had broken up and were trying to reconcile," Detective Richard Laursen said.
Williams worked at the hospital for 23 years, hospital spokeswoman Shelley Lotenberg said. "Our sympathies and prayers go out to the family, friends and colleagues," she said.
Smith said Williams' son, who rushed to the hospital after hearing of the shooting, was struck by a car while crossing the street in front of the medical center. His name and condition were not immediately released.
Wolfe is a correction officer of 19 years who worked the midnight shift supervising inmates at the county jail next to the hospital, said Liz Consolo, a spokeswoman for the Nassau County sheriff's office. She was not scheduled to work on Wednesday morning, the spokeswoman said.
Consolo declined to comment on Wolfe's disciplinary record or any other details of her employment.