Flagler County sheriff's deputies found Melba Doshier's body Tuesday in the car parked at a Wal-Mart in Palm Coast after shoppers reported a bad smell coming from the vehicle.
The St. Johns County medical examiner on Wednesday said she died of natural causes at least five days before she was found.
Doshier's daughter Alicia, who officials said is in her mid-30s, has been questioned and hospitalized for psychiatric observation.
She was found in the store Tuesday, 13 hours after security cameras spotted her parking the car and entering the store at about midnight Monday.
Sheriff James Manfre said he wasn't planning to file charges.
"This is as strange and as bizarre a case as I've seen," Manfre told The Daytona Beach News-Journal.
Capt. David O'Brien said it isn't clear if the woman meant to come to Florida. Manfre said the woman's state of mind is such that detectives can't take her words for the truth.
Detectives say the mother and daughter lived in Covington, Okla., about 75 miles north of Oklahoma City. They were evicted from their home and left Oklahoma a couple of weeks ago in a car registered in the name of Alicia and Melba Doshier, the sheriff's office said.
Amy Grantz, a Covington resident, said Alicia's father was a high school science teacher. She said after the father died, Alicia and Melba liked to travel across the country.
"They've lived here forever," Grantz said. "You don't see them out and about a lot."
Garfield County Sheriff Bill Winchester said Oklahoma authorities are trying to obtain a search warrant for the Covington residence.
Winchester said searching the home could help authorities determine why Alicia Doshier went to Florida.
"At this point, there's too many ifs as to what might have happened," he said. "I think well know a little more once we get into the house."
Receipts in the car indicated the daughter drove through Texas and North Carolina before reaching Florida, O'Brien said. The woman said she talked to the body during the trip, he said.
While the medical examiner reported the body had been decaying for at least five days, O'Brien said it was probably 10 days.
Detectives found the daughter after the body was found in the parking lot.
"She was in the store shopping," O'Brien said.
Her cart was filled with groceries, children's clothes and other merchandise, he said. The sedan was filled with newspapers, a suitcase and trash, partially covering the body.
The daughter can be held up to 72 hours under state law to make sure she's not a danger to herself or others, and longer if doctors think it necessary.
Manfre said the woman would be free whenever she's released because no crime has been committed.