most children respond very well to a strict routine, and a high level of predictability (like at school for example).
So fixed meal times, fixed bed times, in the evening the same routine, for example at 7:30 time to tidy up, do teeth, bedtime story, read in bed for 15 mins, light out.
Also with behaviour, I give one warning then it is "time out" in his room until he comes down to apologise. It's the same every time, so he now knows the rules. It helps enormously.
It sounds very old fashioned and would not have been my "natural" style of parenting, but I had a volatile 6 year old (we had to move house a few times, which made him feel really unsettled) and I just really needed to bring in a routine.
He knows where he stands, and has calmed down a lot. I could not quite believe how much children crave a level of stability.
Is there anything you can do to make her feel more "settled"?