My son's hair is curly and coarse/dry, like mine. It forms dredlocks in the back if it gets too long! We use kids Suave shampoo-conditioner (all-in-one) and that works well (I have used it in MY hair which is long, and it works well enough for me in a pinch). For dry and brittle hair, you can try washing it less - we usually wash our son's hair once or twice a week, and the other bathtimes it may or may not get wet which is fine. (I don't wash my hair every day either). Also we use a suave spray-on detangler, right after his bath and do lots of combing. The combing/brushing will loosen up oils in the scalp and that's good to maintain healthy hair. You're not supposed to brush wet hair, just dry hair, I think. We wet his hair in the mornings and use the spray-in detangler then too. I think your daughter is old enough to try a grown-up conditioner. I've had good luck with Suave products (inexpensive), Pantene (middle price). Use a conditioner for dry (or curly, which is usually dry) hair. Also I like Paul Mitchell The Detangler OR The Conditioner, but that can be more expensive. Hair can change over time, too, so it may not be a medical mystery (as posted below) - my hair went from being straight and very blond until I was about 7, to becoming extremely curly, dry, and enormous starting at about 7 (as an example).