But the person wasn't an intruder; it was her 27-year-old daughter.
The woman fired one round, but police didn't say where the bullet hit the daughter. She died at a hospital.
The shooting appears to be accidental, police said. An investigation is ongoing.
"The homeowner's story is consistent with the physical evidence and the witness' statement," police said.
The woman's husband is a former undercover narcotics officer with the St. Cloud Police Department.
In a recording of the 911 call provided by police, the husband tells a dispatcher that his daughter has a pacemaker and heart problems. She had passed out, he says. He does not mention a gunshot.
After getting instructions to start CPR, the husband leaves the phone and a woman frantically talks to the dispatcher. The daughter is still breathing but very slowly, she says.
About five minutes into the call, the dispatcher tells the woman that paramedics should have arrived.
The officer, a 17-year-veteran, is on administrative leave but is not under investigation, the department said.
The mother is a 911 dispatcher for the Osceola County Sheriff's Office. St. Cloud is south of Orlando, in central Florida.
Police have asked the media not to identify the family members involved for safety reasons because of the husband's past as an undercover officer.