You should probably see a dermatologist but...!
My son is the same. Fortunately, with his short coarse/dry hair, we have more options than a girl with long hair might.
For sure switch shampoos. Anything without the lauryl sulfates. We like Burt's Bees. But for when the scaly factor peaks, we go w/Neutragena either their T-Sal brand (milder) or T-Gel which is a little more "industrial".
Sunlight is good (again, long thick hair can be a burden). We also sometimes rub Aquaphor into the scalp, leave it (my son's hair is so coarse/dry that even this doesn't make it look greasy) and then shampoo. While the shampoo is soaking in, we use a pretty fine tooth comb to remove the dead skin that has been loosened by the Aquaphor.
Scalp massage can help too followed up with a thorough combing.
Hmmm...Maybe Vitamin E? Or fish oil gel vitamins. Those both improve skin health.
I also got a recent recommendation from a friend whose boys both have excema. It was a skin/scalp oil by Aveeno but I cannot remember the name...