Her mother, grandmother, friends and teachers worried there was something troubling about the girl's relationship with her stepfather.
Yet none of them reported their suspicions to the authorities.
Finally, four years after the sexual abuse began, the girl used her stepfather's own shotgun to kill him.
Distressed and fearing jail, she dismembered his body, burying the torso in a shallow grave in the backyard and dumping his limbs and head at a campsite close to their north Victorian home.
She later told police her act was impulsive. She had "just wanted him to go away".
The girl's tragic story prompted a Victorian coroner on Friday to call for an education campaign for parents of all school-aged children on preventing child sex abuse and for the education department to train teachers to recognise the signs.
State Coroner Jennifer Coate noted there were barriers to the reporting of abuse, such as fear of the perpetrator and a lack of faith in the system to protect people.
"An effective intervention may not only have stopped the abuse of (the girl) but prevented the death of (the man)," Judge Coate said.
The Victorian Coroner's Court heard on Friday the man, who cannot be named to protect the girl's identity, had regularly sexually abused the girl, often at gun or knifepoint, at their home in Mooroopna, near Shepparton.
The girl did not report the abuse to anyone, telling police: "He'd always say that if ever I told anyone ... he'd find me and kill me."
On March 13, 2008, the man pointed his shotgun at the girl and forced her to perform a sexual act.
When he turned his back, she took the shotgun and shot him in the head.
She was arrested days later and charged with murder, but the charges were dropped in 2009 with the Director of Public Prosecutions saying a jury would be unlikely to convict her.
Judge Coate said on Friday the girl's friends and their parents had separately raised concerns with teachers at her school, but no official action was ever taken.
The girl's grandmother also spoke to a teacher about her fears that there was a sexual relationship between the girl and her stepfather, Judge Coate said.
One teacher told the inquest she had believed the comments she heard about the relationship were "just gossip".
Her mother had feared the worst but was met with derision and abuse from her husband and a wall of silence from her daughter.
"Despite the suspicions and concerns held by a range of people, no person made a report to police or Department of Human Services (DHS) Child Protection, nor sought advice from either of these agencies," Judge Coate said.
She noted a number of adults in the community described the girl as a "bright, capable and a focused student" with no obvious bruising or injuries.
Judge Coate said this may have led people to assume ultimately no abuse was occurring.
"One of the important findings to come out of this investigation is the need to be constantly vigilant and challenge our assumptions about whether or not abuse is occurring," Judge Coate said.
"By its very nature, childhood sexual abuse is an insidious crime. Those who perpetrate it typically go to great lengths to avoid detection.