She says she was "desperate for drugs" by October 2010, when she received a late-night message from David Bagster, boyfriend of her friend, Valmai "Jane" Birch.

Bagster was proposing sex and "his version of bondage", with he and Ms Birch, in exchange for drugs. Ms Williams took two Xanax tablets to "give me the courage" before arriving at Ms Birch's Woonona home by taxi about 2am, she would later tell a Wollongong District Court jury.

She described stepping inside the house to find Ms Birch crouched in the corner of a room, with her bloodied hair covering her face and her wrists and ankles bound so tightly her extremities were turning blue.

"I saw her crumpled ... She had her head down. She had very long hair and part of it was dark - it looked like blood - and her feet and hands were a blue/red colour - like there was no circulation," Ms Williams said in evidence, on Monday.

"There was some sort of string or rope holding [her] wrists to feet.

"She wouldn't look at me."

Read more: Jury hears new details in wheelie bin death of Woonona's Valmai Birch

Bagster is on trial for manslaughter, accused of unlawfully killing Ms Birch several months after the encounter Ms Williams describes. The 34-year-old's decomposing, hogtied body was found face-down inside a wheelie bin at her Woods Avenue unit on March 22, 2011.

Multiple witnesses have given evidence of seeing Ms Birch with injuries including a black eye and sometimes severe bruising to various parts of her body in the months leading up to her death.

Ms Williams choked back tears in parts of Monday's testimony, conceding she never contacted police or sought help for her friend the night she found her injured. She said she found Bagster elsewhere in the house that night and left soon afterwards, walking all the way home to Fairy Meadow.

"I said something about drugs - 'you haven't got drugs'. ... I used it [the lack of drugs] as an excuse to get out of there," she said, later adding she was "terrified" of Bagster.

"You didn't try and help Jane?" defence barrister Scott Fraser asked.

"No. I abandoned her, and I regret it."

Ms Williams said Ms Birch showed her marks and bruises on her body when she saw her several days later, but that her friend "was wearing a nice top and seemed happy".

That was the last time she saw her alive.

Ms Williams described Ms Birch as "a very kind and very gentle woman", who could be both strong and vulnerable.

The court heard Ms Birch's mother had died when she was young and her father wasn't part of her life, and she was the recipient of a trust fund.

"She was very easily taken advantage of because of her extra trust fund money," Ms Williams said in evidence. "She was very fragile, but strong. It was an interesting mix. When it came to people she worked for, she was strong in that area. But when it came to people who weren't a client, she was very easily manipulated."

She told the court Ms Birch had stopped working as a sex worker, secured housing in Woonona and was on the methadone program in the lead-up to her death.

In later evidence Monday, an acquaintance of Ms Birch's, Teena Costa, described seeing Bagster run towards Ms Birch at Wollongong''s Piccadilly Centre, screaming at her to "give me my money" before slapping her across the face.

She said Ms Birch "seemed fine" when she visited Ms Costa's sister Leonie's house in early-March 2011 to buy marijuana, but that Bagster returned without her about three weeks later, slurring his words, talking quickly and frothing at the mouth. Ms Costa told police Bagster laughed and replied, "haven't you heard?" when he was asked where Ms Birch was.

"He said, 'we got on the pills last night and I bashed her in the bath tub. I couldn't get her out so I put her in the wheelie bin'," Ms Costa later told police, in a statement.

Asked in court whether Bagster was laughing at the time, she replied, "yes, I thought he must have been joking".

Ms Costa said she learned of Ms Birch's death about two weeks later.

Under cross-examination she was challenged on her timeline of events and other details, asked how Bagster could have been refering to the events of "last night" if Ms Birch's body had already been found.

"Were you aware that Jane's unit didn't have a bath tub?" Mr Fraser asked.

"No," she replied.

The trial continues.