Now, 36 years on, she has spoken publicly for the first time about the terrifying night her father George, 49, 48-year-old mother Iris and brother Philip aged 20 died in a hail of bullets after Williams ran amok with two pistols in Andrew Road, West Bromwich on October 26, 1978.
Incredibly Jill survived her injuries during the slaughter that also left Judy Chambers, another of Williams' neighbours, seriously wounded.
The killer sprayed the street with bullets and hurled a makeshift bomb that did not explode as he fled in his Ford Capri, later shooting dead shop owner Michel Di Maria, and his wife, Lisa, at their convenience store in Nuneaton, before being cornered and arrested in Bakewell, Derbyshire, after a 100 mph police chase.
Jill today recalled: "I was doing my college work sitting in the lounge with my mother on an ordinary Thursday evening just after tea. My brother was in the drive working on his car with my dad.
"Suddenly my brother burst in clutching his arm. He was shocked and wide eyed as he told us that Williams had shot him and my Dad. I tried to scream whilst involuntarily running through the door to go and help my Dad.
"I had just opened the front door with my mother right behind me – she had picked up the phone to call the police I guess – when Williams entered the house through the back door shooting me in the back as I tried to go outside.
"I was shot once under my arm as I turned, four times in my lower body, once on each arm and once in the leg. I was lying bleeding and incapacitated in the doorway while behind me I could hear my mother gasping for breath as she must have been shot too.
"As I lay there I could hear her breathing getting more and more faint until it was no more. Not able to stand, I desperately crawled just outside in the doorway while fighting to stay conscious. As I lay there more shots echoed in the darkness and as my front window shattered, my brother came crashing through, his body resting motionless beside me.
"He had been hiding behind the settee. Williams must have just walked past my mother and I after shooting us and shot him. I passed out for a short time but when I came around I struggled to move and somehow reached to the driveway. I prayed my father was alive but scrambled further down the drive in hope of getting help. I became aware of a crowd gathering at the end of my drive.
"One man came forward to reassure me that an ambulance was on its way as my dad had been taken in the only ambulance that had been immediately sent to the scene. The situation was greatly miss calculated.
"Although I had lost a lot of blood and my injuries were very severe, somehow the brilliant doctors managed to save my life, although they did say that I may not be able to have any children. Judith was also very badly injured but survived."
Williams was was ordered to be detained in a secure mental hospital indefinitely for the 1978 outrage when he appeared at Stafford Crown Court and admitted five cases of manslaughter on the ground of diminished responsibility.
A mental health panel ruled it safe to release him back into the community 15 years later. He changed his name to Harry Street and astonishingly was allowed to settle in Birmingham just miles from where Jill was living totally unaware of the developments.
She said: "My aunty telephoned to say that the press had called her to comment on the release of Barry Williams later that day in June 1994.
"My blood ran cold as my mind raced with all of the horrors filling my head. Oh no he is going to come to kill me and my family, I thought."
In fact Harry Street targeted Warren Smith and his family who lived next door to him at his new home in Hazelville Road, Hall Green. When police raided the address on October 14 2013 and found a a cache of weapons alarmingly similar to the arsenal of guns and explosives he had used in the 1978 carnage. Mr Justice Blair said a fresh tragedy had been averted by 'a narrow margin.'