How old is your puppy? If she's not too young and in danger of hypoglycemia, I think most picky eaters have a correctable behavioral problem and are usually in need of some tough love--pick a good, nutritious food and just go with it.
This same problem has been discussed numerous times on this forum, including here:
http://www.yorkietalk.com/forums/yor...ot-eating.html
Good luck!