“Sounds fishy” Agree.
It’s not the only way. Put someone in a chokehold from behind with your left hand and write a B on their face. It will be backward if you write on the person’s face like you would a piece of paper.
If she was trying to fake this and messed up with a backward B, she probably would have said, Oh crap. I did it backwards. Also, the fact that she used B and not O also makes me think this is legit. Someone this politically minded would have used O, not B.