Help my girl keep chewing her hair

[Chowluvver]

Hello , need some help , I have 1 year old who's currently keeps chewing her hair on her behind and back legs , I don't know why she eats Ava hypo allergic white fish kibble and wainwrights went food which is also hypo allergic brand , don't know why she keeps nibbling herself and we use oatmeal and cocamelon shampoo on her , our others dogs don't have this issue and was wondering what it could be ?