I do think you and your daughter need to get some professional help. I am not saying this to be unkind, but because no one over the internet can give your the answers you seek. We can make suggestions.
I will stick with my comment. When you allow your child to pick the battle, you are in for a fight that may or may not have any basis in reality.
You said she complains about meals. If you know that she is just picking nits -- either completely ignore her comments and redirect the conversation to another topic (I'd never suggest not talking to your child), or provide her with another option. "You can make cereal, if you like." Be careful with food battles. This is an excellent reason to see a professional.
A reward system can work. The child earns a happy face on a chart for every 15 minutes they are acting with a minimum of courteous behaviour. You do not want to be too critical in the beginning because her success is yours, too.This earns her something she likes, like the TV or an extra activity -- perhaps you draw with her without her siblings, or you read to only her. Plenty of parents have had to remove the TV and other electronics from availability. Yes, it is a hassle and yes it affects everyone, but a little peer pressure won't necessarily hurt. Just don't allow a situation where everyone is against your daughter. The sibs can also go on the same reward system -- in fact, they should.
This won't be easy but you have to grow a thicker skin. Everytime you leave your hub to deal, you are telling the kid that she won and punishing the only other person who understands. So try rewards and just not arguing. No audience and your daughter will soon stop. She wins when she makes you mad or upset.
I will also warn you that once you decide on a course of action you have to stick with it and that -- it will definitely get worse before it gets better.
Best of luck.
