This is one thing I found:
My Dog Has Dark Skin Patches -- What Is It?: : Pet Health
But based on the google search, it could be any number of things. For some reason, I want to ask if your Bambi is older. I vaguely remember my Charlie's skin darkening in spots too (though didn't lose hair).
Has she ever had allergies? That was my initial thought. Sounds like may need a visit to the vet...
Good luck.