My dd is like that. She has "busy brain" and just has difficulty relaxing both mentally and physically in order to fall asleep. It used to take her up to 2 hours to fall asleep (and, due to her anxiety, sometimes still does). We found that it helped a lot to teach her to relax her body, through guided meditations and relaxation exercises.
Also, there's a great book called Sleepless In America
which has a lot of information about helping kids get more sleep, from tweaking their daily routine, to exercise, to when to shower/bathe in order to get the body ready for sleep, to relaxing/reducing stress. Just good stuff for me to know, which was helpful even when my oldest was 7/8 and I had to younger kids and thought I couldn't learn more about kids and sleep. YMMV.
This book is full of great guided meditation scripts: http://www.amazon.com/Starbright-Med...ref=pd_sim_b_1
With my dd at that age, I read them to her. Eventually, I made up my own guided meditation stories to tell her. She loved that-I just made sure to incorporate a lot of relaxing imagery. Usually I'd tell her a story in which she was a fairy or butterfly, and she'd fly through some place and see lots of color, feel the breeze on her skin, etc., then land and fall asleep. Simple and relaxing.
This one has both some guided meditation scripts, and some scripts/instructions for learning relaxation exercises like belly breathing and progressive muscle relaxation: http://www.amazon.com/Relaxation-Str...mm_pap_title_0
What my dd likes best, at this point in time, are CDs or audio tracks on ipod. This CD is really good, and is basically progressive muscle relaxation and visualization (it is geared, maybe, toward kids slightly younger, and includes a lullaby-but mine still liked it at age 9):http://www.amazon.com/Floppy-Sleep-G...sr=1-1-catcorr
Guided meditation/visualization we've downloaded from iTunes:Time Out for Dreamers podcast
, Patti Teel (free)Guiding Star Meditation
from Meditation for Children and Teens
podcast by Stin Hansen (free)Rest and Sleep: Help Child Drift off to Sleep Feeling Calm and Reassured
by Lynda Hudson ($-whole audiobook)Relax Kids Nature: Enchanting Meditations for All Ages
($-available as single tracks-each track is a single meditation lasting about 4 minutes)Guided Meditations for Children: Journey Into the Universe
by Chitra Sukhu ($-available as single tracks 7-10 minutes long)