THis problem is way worse than mine but i had something a little similar, I had a crew member that was Bipolar and was constantly in a bad mood, or yelling at someone. I tried everything... yelling back, threatening, calming. everything you listed, but nothing worked, finally i just gave up and it stopped. Her thing was when some gave her attention she got nervous and thus created a huge dramatic scene. So my solution was to ignore her and when it was appropriate to talk to her or i need something from her i acted like it didn't matter if it got done or like i could care less. She is now one of my mose dependable crew members, i just gotta deal with her the right way.
As for your situation, idk if ignoring the situation is really going to solve any problems.