M.S.
You know, my daughter, who is 3, is also having trouble sleeping. I think part of it is that it gets increasingly light at night, and the atmospheric conditions have been wierd this week.
I know that when I have had trouble sleeping as an adult the more I think about it the harder it is to sleep, so my heart is with her! I never go to bed early when I have had insomnia the night before because that is what happens. The long-winding down time is a good idea. Maybe allowing her to read in bed for awhile before she lies down could help, too, because it will take her mind off of it.
I like others' suggestions of melatonin, as well.