Adding Tryptophan to the melatonin might help. I have trouble getting to sleep too due to adrenal fatigue and melatonin+tryptophan have helped a alot. You could try putting some (maybe a 1/4 to 1/2 capsule) in some yogurt or applesauce with dinner.
What's her bedtime routine? When my daughter was that little, I'd give her a bath around 7pm -- a nice warm bath and then she'd have a snack if she was hungry (she'd usually have a jar of bananas -- she liked that better than the fresh kind) and then we'd do story and I would sing some lullabies and put her to bed with her music. This routine would usually take around an hour and she'd be ready for sleep by then.