zoo I really feel for you.
I would be really tempted to take everything (and I mean everything) away from her and make her earn it back. Leave her with her covers on her bed and clean underwear and that is it. Every good deed she earns something back, every bad behaviour she loses something again.
Make a really big deal out of praising the others for good behaviour and every little scrap of good behaviour from her. Make sure she gets LOADS of attention when she is doing well, however small the good or however brief.
Lavish attention on the others when she misbehaves and try really hard to ignore her. (May be beyond all human possibility).
Give her a chart where she can earn signatures for making you smile (worked brilliantly on my dd last summer - we had a great time with it) It can be a job, a hug, helping little bro, being funny but in a positive way, doing a good turn outside the house, etc.
I know my tactics sound really, really harsh but she is making you ill and is probably really unhappy herself and would be a lot happier if she had really, really firm boundaries and knew that she could earn praise and make you happy.