A 39-year-old mom from California holiday shopping at Macy’s Herald Square was repeatedly knifed in the back by a stranger as she changed her infant daughter in the department store bathroom during a wild, unprovoked attack, officials said Friday.

The victim was changing her 10-month-old daughter’s diaper in a bathroom at Macy’s flagship store on W. 34th St. near Broadway at about 3:15 p.m. Thursday when Kerri Aherne, 43, rushed in and repeatedly jammed a blade into the woman’s back, cops said. She also slashed her victim’s arm.

The victim’s husband heard the commotion inside the bathroom, ran in, and grabbed the assailant, holding her until police could arrive.

EMS rushed the mom to Bellevue Hospital , where she’s expected to survive. Her daughter, who was just inches from the stab

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