Neutrogena T-gel works really well, but may be kind of chemically. The scabby part sounds more like dandruff than just dry scalp though. There are some natural dandruff shampoos out there with sulfur in them to combat the problem, but I've always found these very stinky and pretty ineffective. You said your daughter has super dry, course hair. I have dry curly hair and have found a GREAT conditioner. It's made by Aubrey Organics and called GBP. I usually get it at Whole Foods, but it can be bought on line. It's really expensive, but worth every penny!! No alcohol or harsh chemicals in it just good fats, oils, aloe, and vitamins. Smells pretty good too! Good luck with your problem.
:) M.