"Truth is I believe I now have no future," the girl said in a victim impact statement read in Brisbane District Court.
As a successful mind coach, Lynch, 68, worked with the likes of former world No.1 golfer Jason Day.
But in his role as a mentor in Queensland, Lynch manipulated the gifted young girl into a sexual relationship, telling her it would help her game.
"Your job involved boosting the self confidence of your clients," Judge Vicki Loury said on Thursday.
"You made her think that what you were doing was in her best interests when it was as far from that as imaginable."
Lynch gained the girl's trust before engaging in multiple indecent acts which escalated from mid-2018 until mid-2019.
After watching a Netflix show the girl realised she was being groomed and began distancing herself from Lynch before tearfully confiding in her father, going to police in December 2019.
Lynch was described as a "pillar of the golf community" during his 10-day September trial.
But he was called a "man without remorse" at his sentencing on Thursday, with his offending having a profound effect on a vulnerable girl.
She now suffers flashbacks, nightmares, hyper vigilance and has been diagnosed with PTSD, failing to finish school.
"Before meeting Sean I loved golf and was on top of the world. After meeting Sean my life changed completely and spiralled downwards," the girl said in her impact statement.
"I no longer play golf anymore or any sport and rarely do anything."
Judge Loury said the girl's golfing talent had now gone to waste, with her swing coach refusing to work with her after she made her complaint about Lynch.
"It seems that she tried to continue to play golf after making the complaint to police but found it impossible because you were present at tournaments," Judge Loury said to Lynch.
"She stopped playing and doesn't play now at all.
"It is indeed a shame that a young woman with such incredible talent was provided such little support in the aftermath of her complaint by those in the golfing community."
Lynch pleaded not guilty to 11 charges at his trial.
He was found guilty on seven - five counts of indecent treatment of a child under 16 under care and one each of grooming and indecent treatment of a child under 16.
Lynch was on Thursday sentenced to three years in jail, suspended for five years after serving 18 months.
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