OT: Horrible ex Boss applying to work in my new Department!

Personally, I don't see where you have anything to lose if you really look at the bottom line, so I think I would go to your new Supervisor and tell her what your past experiences were with this woman.

Maybe put in such a way as you are looking out for her better interests...

Not only talk to your current boss but ask the current boss to speak with others who worked under this woman to find out the scoop.