How Did Black Widow Get Her Facial Injury in Age of Ultron - Avengers Assemble # 14AU

One of the mysteries during the opening moments of Age of Ultron was who or what did the damage on Black Widow's face? It never gets touched or mentioned in the main story though. Avengers Assemble #14 AU.

Spoilers after the cut...

So apparently, Natasha was in San Francisco when Ultron attacked (which is also where we find her during the start of the story). It's also here that her friend George goes crazy after Ultron hijacks his brain via the prosthetic arm that he got from Tony Stark. It's ultimately the hand that slashes Nat's face...

She later gets inside one of Nick Fury's not-so-secret bunker where she works allies herself with Moon Knight who was also in a mission when the attack happened.

She's in a really bad shape here.