Nathan Matthews, 28, and Shauna Hoare, 21, are accused of killing the 16-year-old in a sexually motivated kidnap plot on 19 February.
But Hoare has denied any involvement in moving the remains and said she had no knowledge of Becky's body being brought to her home in Cotton Mill Lane.
She told the jury she was "angry" when she found out when police told her Matthews had confessed to the killing, adding: "I was angry because he lied the whole time.
"All the pain he caused his mum, the impact on his family."
She said she "didn't understand his reasons for doing it".