The court heard K was regularly beaten and also hit with a broom handle – knocking out her teeth.
Her food was limited by Wixon and she could not leave the house and was forced to secretly wash at night, the jury was told.
Officers described K’s bedroom as looking like a “prison cell”, with other bedrooms untidy and dirty.
She told police: “I don’t want to be here. I don’t feel safe. Mandy hits me all the time. I don’t like it.”
Det Sgt Alex Pockett said when police found K, she was “scared”.
“When the police arrived, the victim had her head held down, it was clear she was extremely scared.
“She had short hair, she looked extremely malnourished, she was in scruffy clothes,” Pockett added.
Sam Jones, prosecuting, told the jury: “By the late 1990s it appears the woman disappeared into a black hole. Not a single meeting that left a record or a single sighting of her outside the house.”
Since being rescued, the woman is now living with a foster family, attending college and has been on holidays abroad.
Wixon was released on conditional bail and will be sentenced on 12 March.