but I will be buying her some DOG shampoo or Selsum Blue or SOMETHING to help her dandruff.
Do NOT use selsum blue or any other human dandruff shampoo! It has chemicals that can be left behind on their coat which could be posinous if she licks it off!

As for oils I like Omega-3. I live in the desert, so it's super dry here especially in the winter. Tibby (my cat) will sometimes get problems with dandruff so I add a little Omega-3 to her diet and it works very well.