In times past the captain would offload her and let them sort it out on the ground. Was there a miscommunication of some sort? Why couldn't the purser or chief cabin or whatever have her replaced before departure in CLT?
Even harder to believe she was allowed to operate the return sector.
It's possible that it was only the presence of the Air Marshal that brought this matter to a head.
I'm not suggesting that the Marshal catalysed the behaviour, merely that the Marshal was a competent witness to what might have been considered accepted behaviour by the rest of the crew.
flight attendants had tried to have Snow removed from duty but that American did not replace her