PS For adults, there are products like Mindsoothe that are said to help, St John's Wart and 5htp, although I've never tried them.

I really don't know if they would be suitable for a tenn girl, though. St John's Wart can lead to sensitive skin and light sensitivity and the 5htp can cause drowsiness. I think that diet would be the better way of obtaining tryptophan to make serotonin for a child.