I have had this same issue with my DD from about the same age. She is still an avid reader, reads all the time, she is now 17 and doing VCE. The sleep issue is hard to get through to them. I tried everything with my DD. The one thing that I did find that helped was her stopping reading, having a shower, then a mug of the old fashioned Horlicks....nice and warm, straight after her shower. Not long after she would head off to bed and sleep. It helped her, not even sure that they still have it! Its a different story now though, she could sleep the day away!!