How To Treat White Patches On Skin?

Hi My daughter is 15 and She has White patches on her skin she went to the Gp and they said it was because of her dry skin so the colour fades. She have the patches on her arm and they are really annoying her and they are spreading even though she has used a lot of creams and moisturisers and none seem to work can you please recommend me a good cream or maybe a soap she can use and we are pretty sure it not vitiligo. Thank you.