S.H.
http://www.sephora.com/browse/product.jhtml?id=P241318&am...
Use this brush everyday.
My daughter has it.
It is GOOD and worth the price.
Keep her hair regularly trimmed to get rid of split-ends. Split-ends makes the hair tangle more.
Use a leave in hair conditioner. The brand "Garnier Fructis." My daughter also uses this. It is good. They have various types. Does not leave the hair greasy. It is very light.
Apply the conditioner, THEN, brush her hair, gently. It will take time to get all the tangles out.
ALWAYS brush her hair before going to bed. Put it in a pony tail. That is what my daughter does and she then does not wake up to tangles.
My daughter has long straight hair too.