Interesting, laughing before she hit him. Not laughing when he slapped her back to the future. Yet now I'm laughing. I guess laughter isn't so much contagious as transferable.
She hit him first, he hit her once instead of punching her repeatedly so it wasn't like he's trying to hurt her. She went in for more knowing he would defend himself. She got exactly what she asked for. The fact her friend was recording shows she was looking for a fight anyways.