A Lancashire teenager who turned killer after finding her mother's boyfriend "invading her space" in her bedroom has walked free from court.
Sophie Holbrook, then 16, stabbed Kenneth Embley, 34, in the neck, Preston Crown Court heard.
She pleaded guilty to manslaughter on the grounds she was suffering from an "adjustment disorder" causing an abnormality of the mind.
Holbrook was sentenced to a three-year community rehabilitation order.
She will undergo supervision and surveillance.
A six-month night curfew order was also imposed.
Passing sentence, Mr Justice Holland said there would be "little obvious benefit" in sending her to a young offenders' institute.
The court was told how the single knife blow caused massive blood loss, partially severing Mr Embley's carotid artery and jugular.
Holbrook, now 17, who "bottled things up", treated her bedroom as her own personal space and became "stressed" if anyone else entered.
Her mother, Susan, and Mr Embley, both alcoholics, had a "volatile" relationship, the court heard.
Two psychiatric reports concluded her judgment had been affected at the time of the attack at the family home in Royd Street, Accrington, on 10 January.
She told police she only wanted to threaten or warn her victim, and did not intend to cause him serious harm.
Holbrook, described as "extremely vulnerable", is now living with a stepfather while under supervision by a local authority.
Passing sentence, Mr Justice Holland said: "There you were, a young person, in practical effect with no home, stayed in your bedroom, the rest of the premises a place in which people drank continuously and to excess, where violence was commonplace."