Hi I am asking this for a friend but she dyed her brown hair blonde but the roots are starting to show. How should she redo her roots? Should she just put hair dye on the top? Or can she just put hairdye on her whold head ? She is afraid that if she just does the roots she will miss some and get some on the already dyed part. If she does will it make the part of her hair that is already dyed a different color? OR can she go get it done at a salon even though she dyed her hair herslf?

So in simple words, how should she redo her roots?