A tourist viciously stabbed by a crazed homeless woman inside a bathroom at Macy’s Herald Square had been changing her 10-month-old daughter at the time, sources told The Post.

The 38-year-old mom, who was visiting from California, was in the seventh-floor bathroom with her baby when she was repeatedly knifed Thursday afternoon, the sources said.

The victim suffered knife wounds to her back, shoulder and arm in the unhinged attack that unfolded during the holiday shopping rush at the packed flagship store in Midtown.

A 38-year-old mom visiting from California was repeatedly stabbed by a homeless woman inside a bathroom at Macy’s Herald Square while changing her baby, sources say. James Keivom

The alleged attacker, Kerri Aherne, 43, was arrested on charges of attempted murder, assaul

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