By the time the young woman found herself entangled with the young man she had met earlier on the night of the ball, she had no memory of how she got there.

She knew that she had been kissing him on the dance floor, but after six drinks on an empty stomach she could not remember the journey across the quadrangle of St Johns College to the area known as the tree canopy.

She could not remember the two of them kissing as they stood under the tree canopy, nor how they ended up on the ground.

But giving evidence in the NSW District Court on Wednesday, she was sure she told him to stop.

The man was 20-year-old Jean Claude Perrottet, the younger brother of NSW Treasurer Dominic Perrottet.

He was not a resident of the college and the pair had not met before the night of the 2015 college ball, where he has been accused of raping the woman.

He has pleaded not guilty to three counts of sexual assault without consent.

But the jury has now been posed with an altogether different version of events, whereby the pair engaged in consensual kissing and sexual activity but stopped short of intercourse and ceased contact on the woman's insistence.

Under cross-examination from defence barrister Alissa Moen on Wednesday, the woman was asked whether she remembered kissing the man when they arrived at the tree canopy and that "it was getting quite passionate". She did not.

She did not remember joining him on the ground when he sat down, or kissing him on the neck or whether the two of them said anything very much while this was occurring.

"I don't remember that the whole sequence occurred," she said.

"If it did I have no memory of it so I can't speak to whether I said anything. I don't remember that happening."

According to this version of events, the woman willingly engaged in the activity and instigated certain acts, but after a time she suddenly stopped.

When Mr Perrottet asked what was wrong she said, "I can't do this".

He then reached over, attempted to pull her underwear down and they began kissing again before she finally sat up and said, "I really can't do this."

As they walked back to her room he said, "We weren't going to have sex, you know."

The woman disagreed with this version of events.

Later that night, after Mr Perrottet had left the college, the woman was distressed as she tried to piece together what had happened. One of her friends called triple zero.

Ms Moen suggested that part of the reason the woman may have been upset is because she could not remember what had occurred and did not know whether she had consented to what had taken place.

"I'm suggesting to you that … you've filled in the gaps in your memory with what you're comfortable with, that you feel, 'This is the way things could have gone'."

"I disagree with that."

The trial before Judge Stephen Norrish continues.