First of all, she's looking great in all these pics. Thanks for posting them. I love the way she looks in the black dress with her hair and makeup.
Secondly, I think that's after she's finished a bh. After she's finished over her shoulder and the racquet has rebounded back down again.
Petra tends to release her upper hand from the grip earlier than that on the fh.
She quite likes to slide the upper hand towards the throat as she releases it.
Many two handed players find this a more comfortable position when taking the racquet back for a fh.
I'm actually not sure if that pic is just posed though or from actual play.
If it's posed then she might not be hitting a ball at all.
Anyway, her normal fh backswing with the upper hand movement is visible in many videos, for instance here: