The sister of a woman slain by the Gilgo Beach serial killer is too “psychotic” to be sent to prison for fatally stabbing her mother 227 times, her lawyer claimed.

The attorney, John Ray, told reporters at upstate Kingston Criminal Court Thursday that his client, Sarra Gilbert, “will kill again’’ if sent to prison instead of a psychiatric facility.

“Sarra’s insane. Sarra’s violent. She is extremely psychotic, and in her psychosis, she has been repeatedly homicidal,” he said, according to the Middletown Times Herald-Record.

A jury rejected Ray’s criminal insanity defense, and convicted Sarra (inset top), 27, of butchering her mom, Mari (inset bottom), 52, last summer.

“She killed her mother. She was going to kill her son. She was going to kill her sisters. The chances that Sarra, in a prison, even on meds, will not commit another homicide are very slim,” according to Ray.

Sarra’s sister, Shannan Gilbert, was one of 11 prostitutes who fell victim to the Long Island serial killer.

Ray had argued that the murder of Shannan had damaged Sarra’s mental health.

Shannan’s remains were found Dec. 13, 2011, in a marshy area — near where the corpses of 10 other hookers were discovered.

Cops still haven’t found the killer, but have said they believe he’s a man who lives on Long Island. The victims had been stabbed or strangled.

Sarra, who lives in Ellenville, used a 15-inch kitchen knife to stab her mom, before bludgeoning her with a fire extinguisher and then trying to drown her in its foam.

In the months before the killing, Sarra was arrested after drowning a puppy named Princess in a bathtub in front of her 8-year-old son, and then threatening to murder the boy, too.

That morning of the murder, Sarra had called another sister complaining of “voices” instructing her to hurt their mother.

When Mari came to help her, she was stabbed, Ray said.

Assistant Ulster County DA Emmanuel Nneji agreed Sarra Gilbert is mentally ill, but said she killed because she’s a sociopath — not because she’s insane. He also feels that she’s dangerous.

“I wouldn’t be surprised if she killed again — not because of her mental illness — but because she is a sociopath,” he told the Herald-Record.

Gilbert is scheduled to be sentenced in August. She faces a maximum sentence of 25 years to life.