I've seen plenty of muted rage from her during the trial as she sits at the desk furiously scribbling at testimony she doesn't want to hear, making slit throat gestures towards the prosecutor, staring daggers at anyone who dares to expose her for what she is.
She's had years to build up her head of steam, just like she had years to build up the steam it took to commit such a heinous crime.
Her day in the spotlight is coming to a close and eventually the simmering pot of rage is going to boil over. I would imagine being handed a guilty verdict, much like being shunned in favor of another woman, would set all that rage she'd been channeling in other ways, free.
She's got nothing but her thoughts and a padded wall to respond to right now. It's not a far reach for me to think it's unloading.