Lebanon, Ind. ? A woman who gained national attention last year for impersonating a long-missing girl was expected to walk out of jail early Thursday, less than four weeks after she pleaded guilty in the hoax.

Donna Walker, of Topeka, Kan., was to be released from the Boone County Jail shortly after midnight after receiving credit for time already served and for good behavior, said Jeff Edens, the county’s chief deputy prosecutor.

“There have been no problems with her behavior that would prevent her release,” Edens said.

Walker pleaded guilty but mentally ill April 2 to a felony count of attempted identity deception and a misdemeanor charge of false reporting and was ordered to serve an 18-month term under an agreement with prosecutors. She has been jailed for about nine months in Indiana and Kansas since she surrendered to authorities on July 31.

Under terms of her release, Walker is to serve four years of probation for impersonating Shannon Sherrill last summer through phone calls and e-mail messages.

Sherrill was 6 when she vanished in 1986 while playing hide-and-seek near her mother’s home in Thorntown, about 30 miles northwest of Indianapolis.

Walker, 36, could return to Kansas to serve probation, but defense attorney Michael Gross declined Wednesday to say where she would go after her release.

Walker could have faced up to four years in prison if she had been convicted of the 12 counts filed against her last year.

Walker was found competent to stand trial. But a psychiatrist who examined her concluded she suffers from a mental disorder that compels her to perpetrate “grand hoaxes” to gain attention.

Walker told a judge during a hearing last year that she had been adjusting to new medication for mental illness when she telephoned Sherrill’s father and claimed to be her.