Given that you are desperate the only thing I can suggest is to have a look at her diet. This is a great website www.fedupwithfoodadditives.info if you want to look into dietary aspects. It might help as preservatives can exaggerate bad behaviour. A lot of parents have seen big improvements in behaviour by changing diet, I am one of them. In Australia there is a particularly bad preservative called 282 which prevents mould. I cut this out of my daughters diet with great results.
Give it a try it can't hurt but don't expect any changes for at least a week. Good luck