At times they were left in the sole care of the defendant and it was during these periods that he sexually abused them, she said.
The youth, who lived with the man during the alleged offending, told the jury she came to expect he would want to have sex with her when she was left in the sole care of him.
When asked by Ms Rielly to detail the sexual abuse the girl hung her head as the court sat in silence.
"Is it hard to talk about?" Ms Rielly asked. The girl replied yes.
She went on to describe feeling confused when the man touched her privates and that he had attempted to have sex with her numerous times before full intercourse was reached.
One time when he was touching her a light flicked on outside the house, she said.
"He quickly shut the blind, put his pants back on and ran into the lounge."
She told the court she had also seen the man having sexual relations with two others at the house; one with physical and intellectual disabilities so severe she can't speak.
Under cross-examination defence lawyer Scott Jefferson put to the girl that her allegations were not correct and that she had not initially told police the extent of the alleged offending.
She cried as she insisted, "No they did happen. I was too scared [to tell]."
The trial before Judge Bridget Mackintosh is continuing and expected to last the week.