It took a West Australian District Court jury less than three hours on Thursday to find Douglass Stephan Withnell guilty of having carnal knowledge of a girl and indecently dealing with a child.

But they found his ex-wife Bethany Jayne Gilmore guilty only of the carnal knowledge offence and acquitted her of indecent dealing.

The now 43-year-old victim, who cannot be named, cried as she testified during the trial detailing her abuse.

She said when she was 12, she was taken to a dark bedroom where Withnell raped her on a bed, as Gilmore held her hand and told her to squeeze it if she was in pain.

Withnell also inappropriately touched the victim during a separate incident.

But the jury rejected her evidence that Gilmore inappropriately touched her during a bath when she was five.

The court heard the former couple had previously been convicted of sexually abusing two of the victim's sisters.

Justice Joseph McGrath ordered psychological and pre-sentence reports for Gilmore and Withnell.

He also ordered that they be remanded in custody until their sentencing hearing on February 17, saying he had concerns about granting them bail.

"You have been convicted of serious offences," Justice McGrath said.

Australian Associated Press