E.S.
I was and still am your 7-year-old daughter. Do not go the commercial shampoo route. They are manufactured toward the "annoying" flakes vs. the major flakes.
I would take her to a dermatologist to rule out psoriasis or other scalp conditions. He/she may prescribe Neutrogena or a prescription.
Again, the women they portray on the commercial with a few flakes on their black shirts, hardly cut it.
Good luck.
P.S. Neutrogena works!