The Wisconsin woman who ruthlessly stabbed her sixth-grade classmate to the brink of death as a sacrifice for the fictional Slender Man character a decade ago will not be released from a mental institution.

A judge shot down Morgan Geyser’s request for conditional release from the Winnebago Mental Health Institute — ruling Thursday that the 21-year-old posed a risk of harming herself, others or damaging property.

Geyser had tried petitioning for her freedom by claiming she had been faking her psychotic symptoms over the past decade — which two psychologists testified Wednesday “doesn’t line up” with years of observation and treatment.

“That would be rather remarkable. That would be very callous as well,” said Brooke Lundbohm, who has seen Geyser since 2014.

“If the person is not able to have insight into their mental health condition, the potential warning signs, the triggers that could cause decline, have insight into the kinds of treatment that may be beneficial — it raises a lot of concerns” about being discharged, Lundbohm testified.

Several experts warned that while Geyser has made “bona fide progress” in her mental capacities, she should remain locked up.

Psychologist Deborah Collins called Geyser “future-oriented” and suggested release could be appropriate in six to 12 months.

Geyser was initially sentenced to a maximum of 40 years in the facility in 2018, after she was found not guilty by reason of mental disease for the vicious stabbing of her friend, Payton Leutner.

Anissa Weier — who was also committed Winnebago in 2017 for her role in the attack — was granted conditional release in September 2021.

They were both just 12 years old when they lured Leutner to a Waukesha park after a sleepover in May 2014.

Geyser stabbed Leutner 19 times while Weier cheered her on.

Leutner survived the attack by dragging herself out of the woods and flagging down a bicyclist, with authorities saying at the time that the sixth-grader barely survived the attack.

When interviewed by police, Geyser and Weier claimed they attacked their friend to appease the fictional character Slender Man — a tall, slim, faceless creature that was first developed in online forums and was said to lurk in forests traumatizing children.

Geyser was diagnosed at the time with schizophrenia spectrum disorder.

She pleaded guilty to attempted first-degree intentional homicide and was sent to the psychiatric institute because of mental illness.

Weier pleaded guilty to attempted second-degree intentional homicide and was also sent to the psychiatric center. She was granted a release in 2021 to live with her father and was ordered to wear a GPS monitor.

With Post wires