Shirley was last seen leaving the babysitter's home in Hennessey, Oklahoma during Thanksgiving weekend in November 1980. She left with her ex-husband, Gary Clift, in his car. She has never been heard from again. Two days later, Gary reported her missing; he said she'd run away with a group of Mexican men. Shirley's mother also reported her missing after she didn't appear at the family Thanksgiving dinner. She left behind a baby daughter.

Gary and Shirley married in 1975. It was a second marriage for both. In 1980 they separated, and fought for custody of their baby daughter. Shirley won primary custody. Gary stated he and Shirley had simply drifted apart and their break-up was amicable, but Shirley's mother says Shirley told her she was afraid of Gary. Gary had multiple run-ins with the law in the years following Shirley's disappearance: he was convicted of burglary, possession of drug paraphernalia and driving while impaired in a 1983 incident, and he was convicted of two counts of forgery in 1995. None of the criminal charges involved violence, however. After Shirley's disappearance, Gary became their daughter's primary caregiver. He later took her and moved to Albuquerque, New Mexico.

Nine years later, police discovered Shirley's Social Security number hadn't been active since her disappearance, a strong indication that she was deceased. They located Gary in in New Mexico and interviewed him about his ex-wife's disappearance again. This time he said she was dead. He said they got into an argument in the car about a photograph of their daughter that both of them wanted. Shirley slapped him in the face, he hit her on the head and she opened the passenger door and jumped from the vehicle, which was going about fifty miles an hour. When Gary found her, she was unconscious and didn't appear to be breathing. He said he panicked and drove around with her body in his car for several hours before he buried her in a five-foot-deep grave on the banks of the Turkey River.

Shirley's mother doesn't believe her daughter would have jumped from a moving car. In 1974, Shirley was in a car accident and injured her neck. She narrowly escaped being paralyzed, and doctors warned her she could still become paralyzed from the neck down if she moved the wrong way. Police searched the site Gary indicated, but all they found was a single coat button. Gary quickly recanted his statement and there wasn't enough evidence to bring charges against him. In 1996, he and his daughter met at Turkey Creek and her told her Shirley was "close." In 1999, authorities brought a cadaver dog to the site and the dog indicated the presence of human remains. Investigators uncovered an unspecified piece of evidence that they said could lead to first-degree murder charges against Gary, but then the case became cold again.

Shirley's case remains open and unsolved. Foul play is suspected in her disappearance due to the circumstances involved.