Mollie has dry skin on her back......so much so that her hair looks grey over her back

She had a small amount early january but that seemed to improve,now it is much worse

Mollie has just finished her first season,she is raw fed and has oily fish twice a week,at the moment raw Mackeral

the only treats she has other than raw carrot is a gravy bone after grooming and one when she goes to bed

I use advocate monthly which she had on the 18th Dec and again January.
We are in Spain for the winter and on a camp site....i have given her tap water

She is also out in the sun most of the day
My question is..... does anyone know what could have caused it ? and any advice please.
I have today started giving her bottled water in case it is the chemicals in tap water here. Could it be the sun or the Advocate ??

Any thoughts would be appreciated. Jan