Does your DD have any food intolerences? I have heard of a theory about kids being intolerant to silicitates (tomato, potato, or night shade foods) actually have winding down and sleep dificulties. Basically these types of foods can wake kids up making it hard for them to settle. Just a thought
Mum tried this with her XP's son, he had ADHD. Try the book 'Fed Up' by Sue Dengate - I think it gives tips & maybe an elimination diet? I remember he couldn't have green apples, among other things.