Ester Kline's body was discovered by her husband, David, after he returned from an out-of-state trip.
Authorities believe she may have locked herself out; she had sent her husband a text saying: "I wish the spare key was here." the Cincinnati Enquirer reported.
The window is about 3 feet wide and a foot high.
"It was a narrow opening, smaller than a person's body," police Sgt. Jeff Mitchell told the Middletown Journal.
"Not a whole lot of maneuvering room, because it's below ground in a window well."
Kline became stuck when she tried to get through the window feet first, and scuff marks on the wall from her shoes indicate she struggled to push herself free, Mitchell told The Enquirer.
"Essentially she couldn't breathe," Mitchell said.
The Warren County coroner's office said the death was accidental.