I was going to say that it happened in Oakland, but noticed this in the article:
A teacher and security guard found the girl injured in the bathroom with Diame and called police. Officials say the girl may have paid the price for a feud between her family and Diame’s.
The child was hospitalized with serious injuries, but is expected to recover. Diame is expected to face charges for assault with a deadly weapon.
Between the female's name and the hint at her culture, I'm guessing she's an immigrant.
But it's still Oakland. Hunter's Point in SF is similarly dangerous. Ditto at least some parts of East Palo Alto (instead of being on the "wrong side of the tracks", East Palo Alto is on the wrong side of US 101 freeway)