A., I have a similar problem with my nine yr old...I personally want to say, see the doctor and ask about the herbal remedies. I love herbals but keep in mind, we made synthetic (lab produced) drugs after finding their "real" drug uses from botanicals. Any herbals can still be dangerous esp when used by lighter wt and younger individuals.
I personally have tried to cut out caffiene, but noticed the past few nights I've had tea with my evening meal and now have trouble getting to sleep. Make sure her last 4-5 hours of fluids are only water. Milk has sugar and can cause problems in kids going to sleep. I know, mom used to give us warm milk to help us sleep and yes it can, but with some children, like my 9 yr old, any sugar will cause alertness. I blame myself, I was addicted to German Coca-cola when she was in the womb! LOL! Now she's very active.
You may even try getting her up no later than 8am. My children have been staying up late and sleeping in since school has let out, but in about 4 days we will be back to our usual schedule. I've studied where children need about 9 to 10 hours of sleep at night. Another thought is how much water is she drinking during the day? Mild dehydration can cause problems with your sleep cycle.
Something that I've tried over the past few months is a 15 minute journal. Each night, I have a pen and notebook by the bed. I write down everything that is on my mind during the 15min, including things I need to do the next day. It helps me to get things "out of my head" so I'm not laying there thinking about them all night! That may be more for adults than an 8 yr old, but it's worth a try. Hope all this helps! Nice warm tea (decaf) may help too. Good luck!