The unhinged woman charged with stabbing a tourist changing her baby’s diaper at Macy’s Herald Square brazenly admitted that she had “wanted to go to prison” — rather than back to a mental hospital — after the grisly crime, prosecutors said Wednesday.

Kerri Aherne, 43, made the stunning confession to cops shortly after she was arrested for allegedly randomly attacking a 39-year-old California mom inside the iconic Midtown store on Dec. 12, a court heard.

“(She) said she couldn’t tolerate hospitals any longer and wanted to go to prison rather than be returned to a hospital,” Assistant District Attorney Paul Barker revealed at Aherne’s Manhattan Supreme Court arraignment.

Aherne, wearing a pink sweatshirt over grey pants, pleaded not guilty to attempted murder, assault and endangering the welfare of a child charges in front of Judge Ann Thompson.

The homeless former home health aide from Massachusetts took a cab from her transitional housing unit at the Manhattan Psychiatric Center to the famed department store, she told The Post in a jailhouse interview.

Aherne said she’s been hearing “voices” in her head since she was six — and it was those voices that told her to “kill someone” at the department store’s flagship location.

“It said that I had to go to Macy’s and kill someone,” Aherne told The Post.

Prosecutors said Aherne purchased a large kitchen knife from Macy’s before heading to the seventh floor bathrooms around 3:10 p.m., where she stabbed the unsuspecting woman in the back as the new mom was changing her 10-month-old daughter.

“(She) looked for someone to kill because voices in her head told her that she had to kill someone or else she would be killed,” Barker told the court.

The victim suffered two slashes on her back in addition to several lacerations — before fighting off and subduing Aherne with her “mom instinct,” a relative said at the time.

The child fell from the changing table but was miraculously unharmed during the bloody attack, according to prosecutors.

Aherne said from behind bars that she had been diagnosed with schizoaffective disorder, which she described as schizophrenia with a mood disorder — and claimed to The Post that she was being “tortured by the government.”

Records show that Aherne was arrested in Massachusetts in 2018 for making online threats, including posts about killing Sen. Elizabeth Warren and “getting a gun” to shoot someone at a police station.

Aherne spent two years locked up in a Massachusetts hospital before she was released and fled to the Big Apple, she claimed.

“She said she left Massachusetts in an Uber in the summer of 2024 while out of the hospital there on a temporary leave pass,” Barker said in court.

While hospitalized at the Manhattan psychiatric facility, Ahearn was administered four medications twice a day, including antipsychotic medication and Prozac, she said.

She was released from the hospital just a day before the alleged attack. But Aherne claimed she didn’t receive her medication after returning to transitional housing on the hospital campus.

The judge ordered Ahearn remanded to jail and for her to undergo a psych evaluation before her next court appearance Feb. 11.

Aherne’s attorney, Kevin Sylvan, said that his client was “frightened, scared and quite apprehensive.”

“She’s in a difficult situation and a difficult state of mind. That’s what we have to address,” he told The Post after Wednesday’s hearing. “We just had the assessment test request granted by the judge for an examination. So that’s where she’ll go right now. That will tell us what will happen going forward.”

Aherne faces up to 25 years in prison if convicted of the top count.