The alleged relationship between McDonald and the inmate isn't an isolated incident at Joseph Harp Correctional Center.
The charges against the former case manager mark the fifth time since 2008 an employee of one of the Lexington correctional centers has been charged with raping an inmate.
In June 2008, a prison secretary was charged with rape after she confessed to having sex with a male inmate at the prison.
Joi Ilene Starr, 31, eventually pleaded guilty to second-degree rape and was placed on probation.
Court documents indicate Starr and an inmate had one sexual encounter in August 2007.
The 37-year-old inmate was convicted of murder in 1992, shortly after turning 18. He's now being held at the James Crabtree Correctional Center in Helena.
Katrina Lavern Hinds, 40, was charged within a month of Starr.
Hinds, who worked at the Lexington Assessment and Reception Center in 2008, was charged with rape after confessing a one-time sexual encounter with an inmate who was convicted of drug charges in 2005.
Hinds pleaded guilty in March 2009, receiving two years probation.
In July, two nurses employed by the Joseph Harp Correctional Center were charged with raping the same inmate — a 34-year-old convicted murderer.
Debra Joanne Harms, 49, also was charged with bringing contraband into the prison for the inmate, including a pouch of tobacco and money.
Kristina Marie Knutson, 30, was charged with rape after admitting to having sexual relations with the same inmate inside a treatment room at the prison.
Sexual relations between the inmate and Harms took place in the same treatment room, records show.
It also was discovered that the inmate had called the women more than 500 times from the prison, court documents show.
Harms and Knutson each pleaded guilty last year, receiving probation.
The inmate is now serving out his life sentence at the R.B. Dick Conner Correctional Center in Hominy.
Starr, Hinds, Harms and Knutson are now registered sex offenders in the state of Oklahoma. Each of the women will have to register for life, according to state records.
Jerry Massie, spokesman for the state Corrections Department, said reports of prison employees engaging in sexual relationships with inmates are relatively rare, usually no more than four or five a year.
“These things happen,” Massie said. “I would say every prison system in the country has to deal with this problem.”