Julz was talking about using moisturizing head & shoulders on one thread the other day and said it worked great. I think the pup was itchy.
Oatmeal shampoo and comb-through conditioner; rinse out; spray-on conditioner.
I've never had one that got dandruff, so this is about all I can think of. Good luck and tell the poor little thing I'm sorry she's got that stuff. It must itch!