Crown Solicitor at Manukau Natalie Walker has told the court Pairama was beaten, tied to a chair and gagged.
Her naked body was also burned with an aerosol can and cigarette lighter, Walker said.
The now 15-year-old witness, who cannot be named, was given immunity from prosecution by the Deputy Solicitor-General in exchange for testifying about what she saw and heard at the Buckland Rd home in Māngere.
Pairama's body was found by police in a steel drum in the vacant Housing New Zealand property on July 8 last year.
Ashley Winter, also known as Toko Shane Rei Winter, 29, and Kerry Te Amo, 25, are on trial, accused of kidnapping, torturing and murdering her.
Winter, a transgender woman, has pleaded guilty to kidnapping but denies murdering Pairama.
Te Amo has pleaded not guilty to both charges.
The teen witness told police that Pairama, who was also known as Precious, was told to strip naked, was tied to a chair with rope, had her hair cut, before chemicals were poured over her and her body burned.
"I was just talking to Precious and I told her [I] didn't wanna hit her, and Ashley got angry, [she] just came in the room and then pulled [Pairama's] hair and then told me to finish her off," the teen told Detective Constable Frageo (Damon) Petersen.
"After that they told me to go to the living room to keep a look out and 'cos they didn't want me to look at it, so I went to the living room, sat there and I could hear like stomps, could hear banging in the hallway and when they finished killing her, one of them came outside and I opened the door and I saw her hanging."
The teen said Winter was "stomping" on Pairama's head, causing a sound "really loud like her skull breaking".
"They told her to take her clothes off and shaved her hair, burnt her body parts and then had a little meeting."
Pairama, the teen said, was "crying ... she doesn't know how to fight ... she just went with it".