My son (12) just began taking melatonin on school nights about 2 weeks ago. He takes 1.5 mgs. His doctor is also aware of this decision. He laso began about 5 weeks ago taking Adderall for his ADHD (he's been treated with Concerta for the past 3 years). Of course with stimulant medications, which I'm not too fond of to begin with, he's bouncing off the walls when it wears off in the evening. Psych recommended CLONIDINE or RISPERIDAL, which I was utterly afraid to try with him, so we opted to try the Melatonin first. Thankfully, when given about an hour before bedtime, he winds down very well. Unfortunately, he's come home from school quite tired and moody everyday, which it's hard to say whether it's from the new stimulant, or the melatonin, so we're not going to give melatonin over the next week, and see if the tired, moodiness continues.
Sorry that I have no suggestions for a child so young. I would absolutely do tons of research, and have a very thorough conversation with her Doctor, rather than just assume it's ok.
Best wishes,
Sue