The weapon had been brought to the Seddon Rd home by another person and Williamson pointed it at Sutcliffe in jest as people at the flat engaged in group sex.
Sutcliffe took the shotgun off him and fired, not realising it was loaded.
Sutcliffe tried to hide the weapon and dragged Williamson's body to the front of the house before calling emergency services.
After telling police false information twice, she eventually confessed that the gun had been pointed at her head before she took it and that she didn't know it was loaded. She didn't think Williamson knew either.
Justice Christian Whata sentenced Sutcliffe to three years and one month imprisonment, saying her behaviour was reckless, but he saw hope for her.
"Your actions were spontaneous and you didn't seek help immediately, but you're now deeply aware of what you have done, meaning you're a prime candidate for rehabilitation," he said.
But Williamson's mother Kathleen Brown, labelled Sutcliffe's actions as stupid, irresponsible and callous.
"We looked forward to the day my son would turn his life around but his violent death has left us reeling because as a mother you don't expect to bury your child," she said.
Her husband, Mervyn Brown, Williamson's stepfather, questioned Sutcliffe's remorse, saying she displayed an arrogant attitude. Sutcliffe merely wanted "her 15-minute moment of fame and to be the centre of attention", he said.
"She was smiling, laughing and waving to her family showing little respect for the man she killed, nor does she accept responsibility for her actions," he said.
Brother Shay McAulay told the court he realised he was supposed to urge the offender to improve her life but he didn't care.
"To me, she is as dead as my brother. I don't care what happens to her."
The Herald previously reported Sutcliffe and her 20-year-old girlfriend had been drinking pre-mixed bourbons earlier in the day on May 31.
Williamson joined them when he got home from work and sometime between 6pm and 6.30pm, a friend of the group, Anthony Brett Clegg - who was recently out of prison - arrived at the house and also began drinking with them.
Anthony Clegg was jailed for two years. Photo / Supplied
A short time later, Clegg, 39, called an unknown associate to get a sawn-off shotgun and shotgun shells. It was put on the kitchen table.
The group then took GHB - gamma-hydroxybutyrate, a class B controlled drug that enchances sex drive - before Sutcliffe, her girlfriend and Clegg went to a bedroom for a threesome.
Williamson then walked into the room holding the gun and, in a manner described by Sutcliffe as "playing around", pointed the gun at her.
She took it from him and pointed it at him before asking if it was loaded and almost immediately pulling the trigger, as the pair stood 2m apart.
After being shot, Williamson replied "of course it's loaded you stupid slut" before collapsing to the ground. He died shortly afterwards.
Clegg has already been jailed for two years for his part in the shooting.
