The year 12 student at MLC School in Burwood Nsw had been studying for the November exams of the International Baccalaureate, an internationally recognised high school diploma.
But today she is dead, stabbed to death by her older sister at their Strathfield family home, police allege.
Emergency services were called to the single-storey Federation home on Mosley Street about 11.30am, where they found Susan, dead from at least one knife wound to the neck. Her 20-year-old sister Kathleen, an MLC graduate, was arrested when police discovered her sister's body.
She was taken to Burwood Nsw police station and questioned until late afternoon.
The girls' parents, John and Maureen, also spent the afternoon at Burwood Nsw police station being counselled by officers.
The acting principal of the Burwood girls' school, Di Cottrill-Dormer, said she would not comment on the death.
"It's in the hands of the police [and] it's inappropriate for me to be saying anything at the moment," she said.
Yesterday afternoon families near the Worralls' house expressed their shock at the almost unthinkable crime.
A neighbour, Laval, 46, said he saw the family quite often, but rarely spoke to them.
"They seemed to be very nice people. I see the father from time to time mowing the grass," he said. "It's terrible … it's hard to believe that something happened here, it's hard to imagine."
Another neighbour, Leon, said the first he knew of the murder was when he walked outside his house
NEW South Wales accused killer Kathleen Worrall is believed to suffer from a hormonal disorder that can lead to an imbalance in the production of adrenalin.
The 20-year-old, accused over the stabbing death of her 18-year-old sister Susan, is a member of two Facebook support groups for sufferers of congenital adrenal hyperplasia, a condition that can be controlled by medication.
Ms Worrall has remained under medical supervision at Silverwater Women's Correctional Centre since her arrest on Friday.
The Facebook sites that Ms Worrall is a member of have closed to new members since she was charged with the murder, with Lelea Propadalo from Congenital Adrenal Hyperplasia support faith group telling members to prepare for negative publicity for sufferers of the disease.
"A young woman with CAH in Australia has been arrested for the death of another person and already some articles are noting that she has a hormonal disorder that causes an excess of male hormones," Ms Propadalo said.
The revelation comes as details of the sisters' state of mind and relationship in the months leading up to the alleged murder appeared on website mydeathspace.com.au
Forum user Vodkasunris posted old status updates from Susan Worrall's Facebook site in May showing her sister was concerned "SOMEONE" was hacking into her Facebook account. Susan was glowing of her older sister, writing that she thought Ms Worrall was, "the best person in the world!!".
"You are smart sexy and you must be the funniest person in the world. I wish I was half the person you are I really look up to you. You are like a god to me," Susan wrote on the website.
Friends of the Worrall sisters paid tribute to the pair yesterday, saying that they were both beautiful girls.
Friend Harriet Allan said: "Kathleen and Susan are both really nice girls and we never thought something like this would happen to either of them."
Susan's high school, Methodist Ladies College, held a prayer service on Saturday to support members of the school community.
"Many will be affected by this tragic loss," MLC's middle school head Di Cottrell-Dormer told students.
Kathleen Worrall, left, who is accused of murdering her younger sister Susan
What can I say
It so sad to die so young
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