How do you deal with this?

So at my old job they hired a girl I'll call Vicky (fairly odd parents for a picture)

She did her job perfectly and quickly but she was fucking weird! She wouldn't talk to anyone but the boss or unless it was about work and she would talk to herself 24/7 under her breath but loud enoghht so we can hear. She was saying really dark shit too but nothing reportable. Just hinting at the possibility she would snap one day and shoot the place up. But only hinting at it like a super villain origin story. One by one everyone started to quit (a staff a 15 only ppl who didn't quit was the old Filipina women 4 of them) including me and she ended up working 14 hours everyday they are opened because they where so understaffed but the only reason they are understaffed is because of her.

And again she did her job perfectly and quickly. She never messed up a order and always kept things cleaned. We all just got scared she was going to come in and shoot the place up.

So what do you do when you have a someone who scares everyone for something not reportable to the point they all quit?