Some bloodlines of dogs are predisposed to vitiligo. Where is she losing the pigment? Is it her nose leather? That's the most common place for it to occur. The dog's body forms antibodies that destroy the pigment cells (melanocytes) and the black nose eventually turns pink. A vet can perform a biopsy on the cells to determine if these antibodies are present, and if so, he can advise you as to any course of treatment he feels may work. Unfortunately, not many treatments are very successful, but to the best of my knowledge, it doesn't affect the quality of life. I wouldn't use the dog for breeding, and of course it could not be shown, but for a pet, I don't think it would affect their quality of life too adversely.
Ghilly
There are various treatment procedures are in used to treat skin condition vitiligo.
But I think for a 3 yrs old baby you should use natural or herbal medicine.
Because there is very rare chance of negative effects associated with these natural treatment.
Today psoralens has been proved very effective substance for vitiligo, It is a natural sensitizer of skin and used in various remedy for vitiligo.
http://www.youtube.com/watch?v=MSyod6EQVtk