Christa Pike

I was a mentally ill 18-year-old kid," Pike said in a statement filed with her clemency petition.

Tennessee plans to execute Christa Pike by lethal injection Wednesday. It will be the state's first execution of a woman in two centuries.

Pike was 18 in 1995 when she and her boyfriend killed a 19-year-old classmate, Colleen Slemmer, at the Knoxville Job Corps campus, according to NPR. Prosecutors said Pike feared Slemmer was a romantic rival. She lured her to a wooded spot, where Pike and her boyfriend tortured and killed her. A satanic symbol was carved into Slemmer's body, NPR reported. Pike is now 50.

She does not dispute her guilt. Her lawyers say a death sentence does not fit a crime committed by an 18-year-old with untreated mental illness and a childhood of sexual abuse. Assistant Federal Defender Stephen Ferrell told reporters Pike was abused starting as a toddler and raped at 11 and 17, and that her trial lawyers never gave the jury that history. Doctors later diagnosed her with bipolar disorder and post-traumatic stress disorder.

"I was a mentally ill 18-year-old kid," Pike said in a statement filed with her clemency petition. "It took me numerous years to even realize the gravity of what I'd done."

Tadaryl Shipp, her boyfriend, was 17 at the time. He got life with the chance of parole. A parole board denied him last year. A third teen involved received probation after admitting to being an accessory.

Robin Maher, executive director of the Death Penalty Information Center, said a jury today would likely not sentence Pike to death if it knew of the abuse she suffered as a child. Nationally, 275 people have been executed for crimes committed at 18, 19 or 20, the center said, though death sentences for that age group have grown rare. Executions across the U.S. nearly doubled last year, NPR reported. The number carried out abroad also climbed.

Gov. Bill Lee said Monday he would not grant clemency. Pike's attorneys have since asked the U.S. Supreme Court to stop the execution.

Slemmer's mother, May Martinez, wants it to proceed. Her daughter volunteered with the Special Olympics, loved roller skating and hoped to work in computers, she told ABC News.

"Every time I think about it, I think about Colleen feeling that pain and trying to get up and run," Martinez said.