Baby shampoo is good on dandruff. I get a heavy weave or highlights of blonde in my hair and the color seems to do ok. Also try using cool or lukewarm water instead of hot when she shampoo & rinse, hot water triggers more dandruff.
Buy a good herbal shampoo containing neem oil or neem extract. This is very good for eliminating dandruff. An alternative is to buy neem oil from health stores and oil hair and wash next morning. This works as well.