"She was hysterically crying, it was terrible," she said in court.
"She was just terrified, bawling her eyes out."
Cook's defence lawyer Roger Crowley pointed out an inaccuracy in the sister's police statement compared to what she said in court. In court, the sister said the complainant told her she wasn't sure if she could call it rape, as she was unsure what sexual activity could be called rape.
The sister told Mr Crowley the complainant said that as she stood on the doorstep and throughout the explanation over the next 20 minutes.
Her police statement, however, says the complainant only said it later in the conversation.
The sister cried as she was questioned and while leaving the dock.