Hi mandy, you could try using frontline spray on your girl or a insecticidal shampoo available from your vets.
Sometimes this dandruff is called Cheyletiella a condition known as walking dandruff but with a good shampoo or frontline it will keep it under control. also i would wash all your girls bedding, I have boxers and mine get it but a course of frontline clears it up, good luck regards polly_45