We have a 7 month old Shih Tzu and she is not too picky with her food. The wife however has spoiled her by hand feeding her though. When she gets hungry she does eat on her own.
I suggest switching to another brand. Right now we are using Wellness Puppy Super5Mix and Ariel loves it. Its human grade food and its baked. When we gave her a sample, she was jumping for it. Highly recommended!!