my puppy had the same problem i switched her food like three times. then my friend told me when she had this problem to sprinkle a little bit of grated cheese on top and mix it up. at first i was a little sceptical about this but as soon as i did it she's eating most of her food all up
so maybe it will work for your puppy as well. once she gets used to it just gradually stop adding the cheese and hopefully she will go back to normal